I quit wow about 1 1/2 months ago. I will tell you that nothing has improved as in Game Play Experience. What blizzard did was take all the old content, slapped a new and improve look and marketed it. Further proof of this is the new 4.2 Heroic Dungeons and Raids, which are using old dungeons which blizzard claimed to say they would never touch, just to wipe them and re-use them.
PvP is controlled by 2-3 classes like always and like every season, one of them is the OP Warrior class. Only different from this expansion from any other expansion and original game: Fury Warrior>Arms Warriors. Blizzard increased Health Pools and for most part, at the start of WoW, people were able to handle the 15 second fight on average between every class. But with gear now advancing players, we have our 3 power houses: Warrior, Deathknight, Mage. Some may say Hunter has moved into position and dropped DK's from their spot, but I didn't see that when I left about 2 weeks after the most recent patch.
Overall, Blizzard made a game that went with lore. I loved the game for the Lore. Cata has nothing to do with Lore because the RTS games ended with the LK and to be truthful, it should have ended there and had an end patch for 3.9 to introduce the Maelstrom incident.
Would I suggest you to go back? No. You quit because you were bored. Stop going back to a game that has already lost you. You don't go back to your wife you divorced or the GF you broke up with do you? There are reasons beyond anything else in the life of gaming: Go Play New Games. Look, there are so many games out there and I know you haven't played 5% of them. Go enjoy something new or an old game.
WoW needs to die and from the claims of the Forums, it is getting its just deserve. The Devs ignored their players too much and they did the same slow fixing and when they did fix it, it wasn't fixed, in fact they caused even more issues. Look forward to the other SC2 expansions and Diablo III because Blizzard's MMO (IMO) is finally dying and I'm happy for this. I want this game to end before I decided WoW was the largest mistake in my life. Aka, worst choice of money use ever.