Cata has been the most fun I've had in WoW since TBC. I love the raid encounters, and feel they're tuned just right. I'm 8/12 on normal modes right now, and figure I'll hit 12/12 right around the time the next tier is released, which is perfect. My guild isn't hardcore, so getting 12/12 normal just before the next tier is precisely where we should be. On top of that, the raid mechanics are actually fun again, after the failures of T9 and T10.
That said, I don't really log on much anymore except to raid or farm for raid mats. Sometimes I'll play a bit with leveling an alt. Long queue times for anyone but tanks really makes gearing up alts through dungeons feel painful. I know it may be less total time than I used to spend hunting up a group, but hunting up a group always felt active, whereas sitting in a dungeon finder queue feels very passive and dull. Plus, with the dungeon finder, I don't know any of the people I'll run with.
Overall, though, I feel like Cataclysm has been a real success.
Kathy, I said, "I'm lost" though I knew she was sleeping
I'm empty and aching and I don't know why
Counting the cars on the New Jersey Turnpike
They've all gone to look for America