Let's see...
Nope. Still my most disliked expansion.
Immersion-wise they made some bad decision. Reducing Uldum to be mostly Indiana Jones jokes was bad (and I LOVE Indiana Jones... I just don't need it my WoW). Vash'jr was a major base breaker for the players. Questing got more streamlined than ever, but as a result you had to do all the quests in a row with little variation, and to get the reputation tabards you needed to grind all the starting quests on alts too even if you didmange to skip one of the zones. LK might've shown up in Northrend all the time in WotLK but with Deathwing they did almost the opposite. Leveling (if we don't count that achievement for getting roasted) we probably saw him most in... Badlands, was it? Whatever, you know the place... and that place was not 80+ content! To someone who does not follow lore outside WoW that might've been even more of a letdown, the advertised villain barely shows up until the last raid tier.
Speaking of the last raid tied... I actually don't mind DS as such, I had some fun with bosses... EXCEPT the last two bosses. Both Spine and Madness were MEH at best, definitely not a fitting end for Deathwing. What's the point of making a giant badass dragon of doom your last boss if your last boss consists of giving him a manicure and killing some tentacles?
If there was one thing I think Cata did better than MoP it was definitely 5-mans for me. I personally actually enjoy doing 5-mans even if I don't need gear/valor/achievements, and MoP definitely disappointed me, but during Cata we got new dungeons at least. Except dungeons were tiered. This would not be a bad thing EXCEPT you were stuck with 2 dungeons for an entire patch (ZG/ZA to be exact) and the fact the dungeons reused environments with previously liked raids that even dropped mounts that subsequently became Lost Forever for those who were unlucky with RNG. Not a good decision, removing two raids people liked to do even if they were old content and making them 5-mans that were initially hard to PUG due difficulty AND making people run those two dungeons for months. LFD and random groups also did not initially mix very well, making running dungeons more of a chore at the launch if you didn't have a guild group, making them a lot less appealing to those of more casual persuasion.
Azeroth revamp was good and bad. On the other hand the old Azeroth had many, many problems, and the new plot lines and quests are better and more streamlined, but on the other hand you lost something "forever" and people generally don't like that. I know I miss old Silverpine for nostalgia's sake even if I really enjoy the new Silverpine too.
It's small things, but it does add up. The fact WotLK was (at least to me) a rather great expansion (and it still holds up as THE expansion I had most fun in, though this fun is mostly because I had a highly sociable guild back then and probably less WotLK in itself) didn't help Cata the least either. I don't really HATE Cata, but I know I took most breaks during it. It was exhausting and felt somewhat unpolished.