Cataclysm. Too ambitious. Lame baddies. Disgusting crispy graphics.
I mean Deathwing was great but they introduced him too fast after the LK. And I would expect a much better fight. Firelands were absolutely disgusting and just an asspull idea to deliver a theme (fire) that would be the direct opposite to WotLK's ice. The devs weren't that smart in those days. Cheap.