I've been going back and clearing dungeons for achievements as I want to have those before the changes in Cataclysm, and it reminds me why I quit after hitting level 60 when the game first came out. The dungeons were too long and often boring as hel. As were many of the raids, with having to clear mounds of trash before seeing a boss, or just having to clear through trash just to get into the instance. That design just exhausts and bores players.