Half Life 2 - Got bored of the game pretty quickly. For me this was overhyped in the manner of ETW.

Call of Duty 4 - there's no reason to play either SP or MP after a while - usual frustations of a mass appeal FPS wrapped up in a shinier package.

MTW II - this was the 'wtf' moment when the TW series started to go wrong for me. Most things were less intuitive than you would expect from a dev team who have had 6/7 releases (games + expansions) to polish stuff. Also - hard to care as much for a less superior game for its time after spending countless hours on MTW and STW.

I thought homeworld was excellent - eye bleedingly hard when games were getting easier so everyone could complete them easily on standard settings.