My friend recently, in fact, in one week alone got into FF14 beta and Cataclysm beta. Since I've been a long time WoW player, he let me play on his account in the Cataclysm beta; and I must say, it's been a blast so far.  I've leveled a Goblin Priest to 37 as Discipline, yes a healing spec, and have enjoyed every moment.  Questing and leveling moves a lot faster even with the changes in the previous patches and is a lot richer in the story telling now. Quest variety has also been pumped up, bringing in new quests like flying around on rocket boots and using them to kill Goblin Zombies rather than just kill 10 Goblin zombies. Player's also get an iconic ability to their spec at level 10, making the journey to level 60 more enjoyable, for example: I was leveling a dwarf shaman and up to level 10 I was using a combo of lightning bolts, melee attacks, and occasional healing. But at level 10 I chose enhancement and got access to Dual wiled and a new weapon attack. From then on I feel like an enhancement shaman, mostly because the play style is more on par with my new specializations. Talent trees were also slimmed down, which a lot of players are complaining about. But I can assure you it's quite alright from the leveling and raiding perspective. Since the trees are slimmed down, each point into each ability does a lot more. There are no more 5 rank talents to deal with. A slight downfall is that you only get a talent point once every 2 levels or so, alternating between new ability unlocks and talent points each level. No more spell ranks too, which is nice since my spells and abilities always scale with the content I am facing. Gear also saw some changes, like the removal of attack power and spell power which is now derived from agility, strength, and intellect. They are all 1 for 1 for conversion, except for the first 10 points. Some classes get double the attack power from strength or agility, like warriors and rogues. Last but not least on Cataclysm changes, this one ties in with the story telling element, is phasing. Blizzard went crazy with the phasing in Cataclysm, allowing the world to change behind your very back (quite literally) as you do quests.  
I can say for sure that Cataclysm will change the way people look at WoW. It's easily worth the $40 (Price may to change) this early in the beta. I haven't decided if I want to level new characters or my current level 80's yet...it's just that fun. That's all I have to say off the top of my head, thanks for reading!