I got AC: Rev a few weeks ago, and managed to beat it a few nights ago.  I have thoughts on the game:
 
1.  Their dumbing down of the property/notoriety stuff bugged the shit out of me.  Basically, whenever you buy a building (bank, doctor, landmark, etc.) you gain 25% Templar awareness.  Every single time!  And as opposed to AC2 or Brotherhood, there's no wanted posters to find.  The only ways to decrease your notoriety is to bribe a herald (25% decrease), or kill an enemy official (50% reduction).  This is a huge pain in the ass, because sometimes you can't find heralds, or if you're at 10% suspicion they won't activate, until you're at 15%.  The system in the previous games worked, so why did they break it?
 
2.  Speaking of broken systems, ALL the treasure chests in the game and the bomb making stuff.  Yes, making bombs is kind of cool, but they're not really used much.  In Brotherhood, you find dozens of random crap in treasure chests or on bodies.  Jars of Leeches, coins, or the like.  This was used as currency to complete shop quests and gain access to shop upgrades.  Now, there's no shop quests, or loot.  All you find in treasure chests are bomb making parts (either casings, gunpowders, or ammo).  And there is a LARGE number of chests around.  So it ultimately serves to weaken what Brotherhood set up, with having you try and track down every chest you could find, to see if there was anything valuable inside.
 
3.  Lack of good characters -- There's Ezio, Sofia, Ahmet, Piri Reis, Yusef, and Suleiman.  There was also a Romani woman who was around for one mission.  That's about it, in Ezio's tale.  No Thief leader (like La Volpe), or Mercenary leader (like Bartolomeo).  There is Yusef who is decent, but he isn't around for a lot, and meets a fairly ignoble end.  Sofia is a good character, as is Suleiman, but both are a bit hollow.  Piri sucks though, and you only have one mission with him.   There's also some swerves in the story (with Ahmet) that are a bit too convenient for the plot.
 
4.  The Assassin's guild stuff is kind of boring now.  It wasn't great in Brotherhood, but you kind  of bonded with those characters.  In this game, they are literal disposable people, that once they reach a certain level you're supposed to either force them into taking over a city, or having them take over an Assassins den.  After you cut them loose, you just pick up more and  more, repeating the process.  Because of this, there is *always* missions to do, because the game never really wants you to stop grinding out levels for them.
 
5.  Plot was fine, but the ending bugged me.  It just ended on such a cliff-hanger let down, that I was underwhelmed.
 
6.  Technical problems:  The game kept failing to sync my save games with Ubisoft's stupid uPlay servers.  Also, a few times, on rooftops, guards were clipping through the roof about halfway through.  That's never happened to me in an AC game before.  The only way I could kill them was to shoot them in the head with a weapon.  I couldn't attack them any other way.
 
7.  Some of the chase missions were very cinematic.  One involved chasing a band of Templar's in a boat through an underground temple, while they're in a boat.  Another one was similar to it, as you had to get a key.  There was a lot of great camera work in these few examples.
 
8.  There was kind of a lack of exploring buildings.  Only about two times are you inside a massive building, and have to explore around it, doing stuff.  I kind of miss that.
 
9.  Janissaries are pains in the ass.
 
10.  The data fragments collecting felt super tacked on.  Yes you get rewards for everything up to collecting 50, but that's it.  If you get 100, you just get an achievement.  Yay?
 
11.  They took out cheats for getting 100% sync for a chapter.
 
All in all, I was severely disappointed with AC: Rev.  It just felt tacked together, and not special.  Here's hoping AC3 is better.

I got AC: Rev a few weeks ago, and managed to beat it a few nights ago.  I have thoughts on the game:
 
1.  Their dumbing down of the property/notoriety stuff bugged the shit out of me.  Basically, whenever you buy a building (bank, doctor, landmark, etc.) you gain 25% Templar awareness.  Every single time!  And as opposed to AC2 or Brotherhood, there's no wanted posters to find.  The only ways to decrease your notoriety is to bribe a herald (25% decrease), or kill an enemy official (50% reduction).  This is a huge pain in the ass, because sometimes you can't find heralds, or if you're at 10% suspicion they won't activate, until you're at 15%.  The system in the previous games worked, so why did they break it?
 
2.  Speaking of broken systems, ALL the treasure chests in the game and the bomb making stuff.  Yes, making bombs is kind of cool, but they're not really used much.  In Brotherhood, you find dozens of random crap in treasure chests or on bodies.  Jars of Leeches, coins, or the like.  This was used as currency to complete shop quests and gain access to shop upgrades.  Now, there's no shop quests, or loot.  All you find in treasure chests are bomb making parts (either casings, gunpowders, or ammo).  And there is a LARGE number of chests around.  So it ultimately serves to weaken what Brotherhood set up, with having you try and track down every chest you could find, to see if there was anything valuable inside.
 
3.  Lack of good characters -- There's Ezio, Sofia, Ahmet, Piri Reis, Yusef, and Suleiman.  There was also a Romani woman who was around for one mission.  That's about it, in Ezio's tale.  No Thief leader (like La Volpe), or Mercenary leader (like Bartolomeo).  There is Yusef who is decent, but he isn't around for a lot, and meets a fairly ignoble end.  Sofia is a good character, as is Suleiman, but both are a bit hollow.  Piri sucks though, and you only have one mission with him.   There's also some swerves in the story (with Ahmet) that are a bit too convenient for the plot.
 
4.  The Assassin's guild stuff is kind of boring now.  It wasn't great in Brotherhood, but you kind  of bonded with those characters.  In this game, they are literal disposable people, that once they reach a certain level you're supposed to either force them into taking over a city, or having them take over an Assassins den.  After you cut them loose, you just pick up more and  more, repeating the process.  Because of this, there is *always* missions to do, because the game never really wants you to stop grinding out levels for them.
 
5.  Plot was fine, but the ending bugged me.  It just ended on such a cliff-hanger let down, that I was underwhelmed.
 
6.  Technical problems:  The game kept failing to sync my save games with Ubisoft's stupid uPlay servers.  Also, a few times, on rooftops, guards were clipping through the roof about halfway through.  That's never happened to me in an AC game before.  The only way I could kill them was to shoot them in the head with a weapon.  I couldn't attack them any other way.
 
7.  Some of the chase missions were very cinematic.  One involved chasing a band of Templar's in a boat through an underground temple, while they're in a boat.  Another one was similar to it, as you had to get a key.  There was a lot of great camera work in these few examples.
 
8.  There was kind of a lack of exploring buildings.  Only about two times are you inside a massive building, and have to explore around it, doing stuff.  I kind of miss that.
 
9.  Janissaries are pains in the ass.
 
10.  The data fragments collecting felt super tacked on.  Yes you get rewards for everything up to collecting 50, but that's it.  If you get 100, you just get an achievement.  Yay?
 
11.  They took out cheats for getting 100% sync for a chapter.
 
All in all, I was severely disappointed with AC: Rev.  It just felt tacked together, and not special.  Here's hoping AC3 is better.

I agree completely with the Janissaries part, they are just so fucking annoying. They aren't hard to kill but take forever to kill without resorting to guns or the like and break your killing flow. The rest of the stuff I mostly agree with, I also found they gave you too much stuff to use. I went through the entire game without using the crossbow or throwing knives. ACIII seems to scaling weapon choices down a bit so that's good.

You make some mistakes in this. You don't cut your master assassins loose. You can still summon them with your signal after they've leveled. All promoting them does is give you 2 assassination missions you can do with the (which is a point for the bonding factor, I'd say) makes them stronger, and stops attacks on their den.

The reason notoriety is harder to diminish is that it give you more encouragement to, well, not do notorious things! An assassin should be wary of getting huge amounts of publicity, yes? Officials and bribe heralds pop up more often than previously, anyways. Guards clip through roofs in every AC game. You've just been lucky enough not to see it till now.

Considering how easy combat is, Jannissaries being hard seems fair.

The data fragments were used to unlock Desmond's first person platforming memories, as well as unlock the outfit.

Overall, I thought that Revelations had a lot more soul than Brotherhood, particularly in its story. I enjoyed all the hints at the modern storyline we got, and I'm excited to find out about Desmond's past, and his father. The multiplayer unlocks showed a ton of new info about abstergo, and even set up an abstergo hit squad who desmond will undoubtedly encounter.

The hookblade was awesome, the bombs were reasonably enjoyable, and very fun to mess around with, and I liked that there were two free-roam locations instead of just one.

The way Eagle sense was implemented seemed a bit rushed at some points, but it was interesting to see Ezio use it for things other than what we've seen it used for in the past, like tracking enemies, or reading a heartbeat. Here's hoping the player has more control over how they use it, if it returns, and that it's just all around sleeker.

Brotherhood and Revelations were a way to flesh out some story and test people's reactions to some new gameplay options, while AC3 was being worked on in the background. However, they were of a higher quality than most games with three year dev cycles I've bought recently. nowhere near as big a step as AC2, but I still feel that they are worth their price. I'm excited for major mechanical overhauls and extended polish time on AC3.

Yeah, trying to go melee killing against the Janissaries is annoying, especially because it's hard to one-shot them, unlike everything else in the game.  A nice lethal bomb works well though.