A couple:
- Spore. It looked so promising, but it turned out to be just a fucking Mr. Potatohead game with some shallow minigames. *deep sigh*
- Brink. It could've worked if connecting to a multiplayer server wouldn't be such a pain. But it just fell apart completely.
- Fallout: New Vegas. The game itself was good, it really had the spirit of the original Fallouts, especially compared to Fallout 3. But my PS3 version of the game was simply so broken that it was barely playable.
- Borderlands. Damn they really fucked up an awesome concept. Diablo with guns? Sounds cool, until you see the same. fucking. scrapyard. for the bazillionth time, and the same damn enemies over and over again, and 90% of all the loot you found was worthless crap.
There are some smaller purchases that turned out to be "meh", but those are el cheapo games I bought during a Steam sale.