After chewing my way through the majority of the new content in Cataclysm, I'm very pleased. This expansion ends some of the bad trends TBC and WotLK followed, while also keeping the feature list as impressive. So what do I mean by "bad trends"? 
 
For the most part, the terrible integration of previous expansions with the base game. Both of them added a big lump of content onto an older game, while not particularly refining the old, rusty elements. Sure, WotLK introduced achievements and several other improvements into the interface, but that's nothing compared to what Cataclysm has changed. Every major feature of the game has been redone, retuned, or just improved to please gamers and encourage them to join guilds, be friendly to each other, and kindly eat their vegetables during dinner. Sure, this won't stop the masses of scrubs and idiots kicking people out of dungeons just because they asked for tactics on a particular boss, but hey, what can you do. PUG's can still be a bit messy if you're grouped with total assholes, but if you're guild happens to be doing a raid/hc/battleground/whatever, and there's enough guildies in that group (50%+), you'll not only receive guild rep and guild xp, but you can also receive bonus rep for normal factions.  
 
Guilds in Cataclysm have actually become a "thing", in that you'll receive perks based on the guilds level, item rewards that can be unlocked by hitting a certain guild level (the cap is 25) and high enough standing with the guild itself in reputation. That last part is a bit messy, since after you hit 85 there's not a whole lot of ways to actually get rep with your guild (dailies and the guild group activities I've mentioned seem to be the only relevant way). Perks are acquired regardlessly of rep standing and you'll get them as soon as you're guild "dings" a specific level (and yes, each level has it's own perk). 
 
The new content in Cataclysm is pretty standard- two new races (Goblins for Horde and Worgen for Alliance), each with new starting zones, 6 high level Cataclysm zones, the level cap increased to 85 and new endgame content to enjoy. And, of course, the biggest improvement: the revamped "old world" with new quests, drastic changes to some zones, mild adjusting done to others. I never thought I'd say this, but for the first time I've genuinely enjoyed questing in WoW. The new quests are interesting and can be a lot of fun. Blizzard has added new quest "templates"- aside from the old fetch quests and kill quests, you'll now be doing vehicle quests in the old world, as soon as the starting zones (some of them, at least). Quest items are also dropped much more generously as well, so forget about grinding in the same spot for that fiftieth wolf hide. The flow and organizing of quests has improved drastically- you'll get a few quests in the same general area, objectives often requiring the same general activity (kill 10 dudes, collect 5 things these dudes drop), you'll turn those in, and you're sent to the next questing area. You'll easily be able to level up from 1 to 60 in a week or two, and then progress to Outland and Northrend. 
 
Which sadly have not been improved in any way. Leveling, especially in TBC (both Outland and the draenei/blood elf starting zones) is still a major pain, and pretty much the complete antithesis of the new, friendly leveling experience. In addition to this, maps haven't been redone (in the old world maps now have flight points and other points of interest marked). It's sad, but hopefully Blizzard will touch those zones in a future expansion, as it would be a huge waste. And the old players love nostalgia.  
 
The new dungeons can be quite a bitch, especially if you've only played WotLK content before. However, Blizzard is significantly nerfing most of the bosses in Cataclysm, as well as buffing a few. I personally liked the challenge heroics offered, and a few weeks into the expansion players were already getting used to the increase in difficulty. Crowd control is a necessity in Cataclysm, and almost every boss has their own gimmick that you'll have to figure out to defeat him. In total, there's 9 new dungeons, including 2 revamped old dungeons- Deadmines and Shadowfang Keep. So basically 7 completely new dungeons, which is a bit low, but luckily Blizzard is planning to introduce new 5-man dungeons with future content patches. There's also 3 new raids, but I haven't had the change to check them out.  
 
Tol Barad is the new outdoor PvP zone in Cataclysm, similar to Wintergrasp in WotLK. While I haven't tried it out either, the massive complaints on the forums clearly indicate there's some balancing issues with the zone. I can't even imagine the lag going on during these fights, although there supposidly is a player cap. 
 
Archeology, while cool at first glance, proves to be a huge disappointment later on. It's basically a secondary skill that everyone can pick up, regardless of your professions (it doesn't count as one, so don't worry about loosing 1 profession slot), and is a game of hot and cold. Every player receives 4 digsites per continent (these are unique to every player, so no worries about loosing nodes to others). Digsites will give you different types of fragments depending on where it is located. For example, a digsite situated on night elven ruins will give you night elf fragments. There are a total of 9 fragment types, and you have 1 active project on each one at any given time. These are generated randomly. You'll be rewarded for the most part with vendor trash, but occasionally you'll get a rare project- mounts, collectibles, and even high level epic gear. This seems like a nice bonus at first, but eventually you'll find archeology to be a sisyphean task . Mostly because you have absolutely no way of getting the items you want to get, I've heard about people grinding for days just to get a particular epic, using up hundreds of fragments in the process. Leveling the skill isn't fast either- you'll get skill points up to 100 skill, then you'll get 5 skill per each project solved, and 20 points per rare project solved. It'll take a LOT of time to get to the maximum level, and an epic flying mount is an absolute must, as you're travelling through the entire world just to get to these digsites. Furthermore, the rewards aren't really anything unique. Certain specs (actually, probably most of them) don't have an epic item from archeology, which is a shame. And I'm sorry, but a cool ground mount isn't enough to convince me to go all the way up to 525 skill. Sadly, the 30 minute dungeon queues leave me wandering completely pointlessly, so I do archeology in that time just for the heck of it. I'm at 436 skill right now, and I'll eventually probably make it to the skill cap. Overall, I don't recommend picking archeology up. But then again, you might as well, because you're gonna be waiting a LOT of time in queues. In the end it's a good representation of an MMO chore.

Cataclysm is probably the biggest WoW expansion yet, and most importantly, it's the most meaningful one. It's an intelligent expansion in that it updates the quintessential elements that needed improving badly, but it also introduces a lot of cool new content to play around with. For the first time, both newbies and hardcore players have something to experience and get out of a WoW expansion. 
 
EDIT: Added archeology paragraph.

After chewing my way through the majority of the new content in Cataclysm, I'm very pleased. This expansion ends some of the bad trends TBC and WotLK followed, while also keeping the feature list as impressive. So what do I mean by "bad trends"? 
 
For the most part, the terrible integration of previous expansions with the base game. Both of them added a big lump of content onto an older game, while not particularly refining the old, rusty elements. Sure, WotLK introduced achievements and several other improvements into the interface, but that's nothing compared to what Cataclysm has changed. Every major feature of the game has been redone, retuned, or just improved to please gamers and encourage them to join guilds, be friendly to each other, and kindly eat their vegetables during dinner. Sure, this won't stop the masses of scrubs and idiots kicking people out of dungeons just because they asked for tactics on a particular boss, but hey, what can you do. PUG's can still be a bit messy if you're grouped with total assholes, but if you're guild happens to be doing a raid/hc/battleground/whatever, and there's enough guildies in that group (50%+), you'll not only receive guild rep and guild xp, but you can also receive bonus rep for normal factions.  
 
Guilds in Cataclysm have actually become a "thing", in that you'll receive perks based on the guilds level, item rewards that can be unlocked by hitting a certain guild level (the cap is 25) and high enough standing with the guild itself in reputation. That last part is a bit messy, since after you hit 85 there's not a whole lot of ways to actually get rep with your guild (dailies and the guild group activities I've mentioned seem to be the only relevant way). Perks are acquired regardlessly of rep standing and you'll get them as soon as you're guild "dings" a specific level (and yes, each level has it's own perk). 
 
The new content in Cataclysm is pretty standard- two new races (Goblins for Horde and Worgen for Alliance), each with new starting zones, 6 high level Cataclysm zones, the level cap increased to 85 and new endgame content to enjoy. And, of course, the biggest improvement: the revamped "old world" with new quests, drastic changes to some zones, mild adjusting done to others. I never thought I'd say this, but for the first time I've genuinely enjoyed questing in WoW. The new quests are interesting and can be a lot of fun. Blizzard has added new quest "templates"- aside from the old fetch quests and kill quests, you'll now be doing vehicle quests in the old world, as soon as the starting zones (some of them, at least). Quest items are also dropped much more generously as well, so forget about grinding in the same spot for that fiftieth wolf hide. The flow and organizing of quests has improved drastically- you'll get a few quests in the same general area, objectives often requiring the same general activity (kill 10 dudes, collect 5 things these dudes drop), you'll turn those in, and you're sent to the next questing area. You'll easily be able to level up from 1 to 60 in a week or two, and then progress to Outland and Northrend. 
 
Which sadly have not been improved in any way. Leveling, especially in TBC (both Outland and the draenei/blood elf starting zones) is still a major pain, and pretty much the complete antithesis of the new, friendly leveling experience. In addition to this, maps haven't been redone (in the old world maps now have flight points and other points of interest marked). It's sad, but hopefully Blizzard will touch those zones in a future expansion, as it would be a huge waste. And the old players love nostalgia.  
 
The new dungeons can be quite a bitch, especially if you've only played WotLK content before. However, Blizzard is significantly nerfing most of the bosses in Cataclysm, as well as buffing a few. I personally liked the challenge heroics offered, and a few weeks into the expansion players were already getting used to the increase in difficulty. Crowd control is a necessity in Cataclysm, and almost every boss has their own gimmick that you'll have to figure out to defeat him. In total, there's 9 new dungeons, including 2 revamped old dungeons- Deadmines and Shadowfang Keep. So basically 7 completely new dungeons, which is a bit low, but luckily Blizzard is planning to introduce new 5-man dungeons with future content patches. There's also 3 new raids, but I haven't had the change to check them out.  
 
Tol Barad is the new outdoor PvP zone in Cataclysm, similar to Wintergrasp in WotLK. While I haven't tried it out either, the massive complaints on the forums clearly indicate there's some balancing issues with the zone. I can't even imagine the lag going on during these fights, although there supposidly is a player cap. 
 
Archeology, while cool at first glance, proves to be a huge disappointment later on. It's basically a secondary skill that everyone can pick up, regardless of your professions (it doesn't count as one, so don't worry about loosing 1 profession slot), and is a game of hot and cold. Every player receives 4 digsites per continent (these are unique to every player, so no worries about loosing nodes to others). Digsites will give you different types of fragments depending on where it is located. For example, a digsite situated on night elven ruins will give you night elf fragments. There are a total of 9 fragment types, and you have 1 active project on each one at any given time. These are generated randomly. You'll be rewarded for the most part with vendor trash, but occasionally you'll get a rare project- mounts, collectibles, and even high level epic gear. This seems like a nice bonus at first, but eventually you'll find archeology to be a sisyphean task . Mostly because you have absolutely no way of getting the items you want to get, I've heard about people grinding for days just to get a particular epic, using up hundreds of fragments in the process. Leveling the skill isn't fast either- you'll get skill points up to 100 skill, then you'll get 5 skill per each project solved, and 20 points per rare project solved. It'll take a LOT of time to get to the maximum level, and an epic flying mount is an absolute must, as you're travelling through the entire world just to get to these digsites. Furthermore, the rewards aren't really anything unique. Certain specs (actually, probably most of them) don't have an epic item from archeology, which is a shame. And I'm sorry, but a cool ground mount isn't enough to convince me to go all the way up to 525 skill. Sadly, the 30 minute dungeon queues leave me wandering completely pointlessly, so I do archeology in that time just for the heck of it. I'm at 436 skill right now, and I'll eventually probably make it to the skill cap. Overall, I don't recommend picking archeology up. But then again, you might as well, because you're gonna be waiting a LOT of time in queues. In the end it's a good representation of an MMO chore.

Cataclysm is probably the biggest WoW expansion yet, and most importantly, it's the most meaningful one. It's an intelligent expansion in that it updates the quintessential elements that needed improving badly, but it also introduces a lot of cool new content to play around with. For the first time, both newbies and hardcore players have something to experience and get out of a WoW expansion. 
 
EDIT: Added archeology paragraph.

I have to agree with most everything said in the OP.  Having done the new dungeons on my healer, tank, and dps'er, I can say that some of the fights HAVE been fairly difficult on healers, especially if mobs aren't killed in the right order or something.  But I like the revamp in difficulty overall.  I like the revamp of the game overall.  I've been having a blast with the game, having come back shortly before Cata but after 4.0.
 
The one thing I am kind of disappointed in is the new guild feature thing.  The current setup rewards guilds that recruit as many people as possible off trade, and kinda screws guilds who prefer to stay small and close-knit.  A guild with 20 characters, 7 of them being 80+, has a hard time even getting to guild level 2, let alone 7 or 8 as many guilds are at.