WoW. I started MMOs with Ultima Online and pretty much ended my affiliation with them after both Dark Age of Camelot and Anarchy Online failed to impress me. I had played Everquest enough by that point and didn't need to play it in a sci-fi setting or with prettier graphics. I gave WoW a spin on the free demo in hopes it was something special and, well....it wasn't.
Sad thing is, I'm a buyer. In Singapore there's probably only like 1 crappy rent service and all the demos are delayed, so I get hyped up because of QLs and reviews. As such, I'm quite an impulsive buyer and will just go out and buy the game and then realize I really hate it and play about 1/4 of it.
2010's Medal of Honor. Good god that beta was awful, people will yell at me for this; but there is no way they can be refined into a good MP experience.
However, singleplayer might pull one out. Still cancelled my pre-order.
And Dragon Age: Origins. Not hating on that game at all, tried it for a good 5 hours, I just realised I couldn't be bothered learning a new rpg world lore.
Oh yeah, and boiling point, that game is hilariously broken.
Lost Planet 2. I really enjoyed the SP in the first and after playing LP2 at a friend's house and seeing how badly Capcom ruined the SP in LP2. I was happy I didn't buy it. The same also goes for Resident Evil 5. As a mostly SP gamer I'm starting to feel like the red headed step child.