Until now it's awesome. Great gameplay. Instances are good to excellent. They implemented enough end game to last a while also. Don't know the difficulty of it. But i do know the got 2 types of heroics, namely expert 1 and expert 2 and you need to farm those to get ready to raid. I can really recommend this game if you are bored with WoW.
Played the beta till level 20 or something, but it didn't manage to capture the same feeling for me. Was ok-ish, but not worth paying 50 bucks + a subscription fee. I'm waiting for Dragon Age 2, now that's going to be an epic game