1) WoW- Cataclysm
Cant really name the other 2 because even though I agree with a lot of posters here about failures, I either knew before they were going to be bad or they didn't interest me in the first place so I never even tried them.
If I had to say 2 more, Id go with Warhammer Online. I expected more from it to be honest and Dragon Age II. It wasn't a bad game, most of the improvements and changes were great and I have no regrets about buying it but it could have been better.