While there's certainly been no shortage of player commentary on how WoW's developed, Gavin's experience as a game developer who's not involved with Blizzard is a pretty unique perspective. I found his article on Cataclysm to be particularly adept at putting into words a lot of things I felt but had difficulty articulating. Most of the expansion's developmental time had to go into a revamped leveling process that few people saw unless they wanted to level a new alt. The content at 85 that greeted more casual players got bottlenecked in a series of difficult heroics that frustrated players dropped constantly.
Personally, I still consider Cataclysm to have been a necessary expansion -- it did a lot of stuff that Blizzard had to do for the game even if it wasn't as eye-catching as what BC and Wrath did -- but I think Gavin's assessment is accurate and measured. (And many of Blizzard's own observations aren't all that different.) Funnily enough, with lots of people leveling new monks in Mists of Pandaria, more people might be seeing Cataclysm content now than they did during the expansion that was actually dedicated to it.
I've linked Gavin's full series here. While it's long, it's an incredibly interesting and detailed read:
- WoW's endgame: Vanilla
- WoW's endgame: The Burning Crusade
- WoW's endgame: Wrath of the Lich King
- WoW's endgame: Cataclysm
- WoW at present: Mists of Pandaria