I quit WoW in october, and I never really killed a major raid boss at it's release or anywhere near after, but I have been playing since Vanilla.
What bothers me, is that whilst WoW IS improving it's questing and levelling experince, the end game is suffering. In Wrath of the Lich King, I could complete ANY heroic, and I was in bad gear most of the time for that, and I never put in a 100% effort in anything, yet I remember watching people raid in TBC, the effort that was put in, the fantastic bosses.. I can see why the raids were the best ever. But I don't think the only problem is Blizzard pandering to casual/making easier raids but the community that played in Vanilla and TBC which is huge have become so skilled that what would be a challenging boss in TBC or vanilla has become easy. It's not just the instanes getting easier but the player bases common skill increasing and people don't recognize this, that's my view anyway.