Wrath certainly feels like the peak of the series. It had a few problems (Wintergrasp being a bit of a mess and the crusader fairground nonsense), but it was lovely, nonetheless. Northrend is one of the most beautiful things Blizzard have ever done. Even Dalaran, that got away a bit from the airport feeling that plagued Shattrath City throughout Burning Crusade.
By killing Arthas, it really did feel like history was in the making, in terms of the lore. We had been fighting his minions and tendril operations since day one, and it felt like putting an end to things, a feeling rather unusual in mumopugers. Even Ulduar felt a bit like tying up lose ends, set in motion in Uldaman and in Ahn'Qiraj.
Of course, then came Cataclysm. It started out on a high note, I must say. Breathing some life back in the neglected Old World and pushing the story a bit. Even if a lot of the story being pushed was rubbish.
The new approach to mechanics was nice, and it all had a breath of fresh air to it. The new zones were great, and it was just so wonderful to feel that the capital city was the new hub of the game. I'll gladly trade that feeling for some lagg. Hell, just the Worgen felt like a peace offering intended just for me.
Of course, then it fell apart a bit.
Deathwing was not and never would be a very interesting threat, and the enviromental disasters didn't really feel like the world-shattering they were meant to be. My favourite zone was the underwater one, because it made you play in three dimensions, so to speak. And all the payoff that the quests were building up to was just dropped. Hell, I wonder if there was some sort of financial emergency at Blizzard, because a lot of stuff simply felt like it didn't recieve the payoff it should. Except bloody Firelands, that kept going and going, like revenge of the Crusade Fair.
And then of course came the stupid "No, Garrosh it totes awesome, guys! We're mean again! CRUSH PUNY HUMIES FOR DA HOARD" business. Alliance really got the short end of the stick, getting their arses kicked on every front at once (because superior Orcish tactics, no doubt) and losing rather cherished settlements left, right and centre. I defected to the Alliance by that time just in spite, more or less. They did say that the Allies moment of awesome was coming, but that is about as likely as them releasing that dance studio of theirs.