The quests are superb. The scenery is amazing. A must have for anyone level 55 and above.
Raiding is great. No longer do you have to be in the "top guild" to see the end game (Naxxramas). Instances are fun and plentiful and don't take an entire evening to clear.
For those complaining about content for new players, I call that ridiculous. If folks are new to the game, they have all the old world and BC content to see. This expansion it targeted at the high level folks. This is what it should be.
Finally we have achievements. These are a nice look at what you've accomplished in game. Think your done with an instance? Try to run it on Heroic. And after that, look up the achievement for it. There are plenty of different things to try and complete for each zone.
They've set the bar again with this one. I look forward to the future patches and future raids.