About the only game I've let Yahtzee talk me into was Painkiller, and that was because I know what good mindless fun FPS can be like. That said, I haven't regretted it - Painkiller is pretty stellar. (Unfortunately, it does make me feel a bit sick to my stomach as some FPS engines will sometimes.)
I like to think I might have influenced him, too. Somewhere on the Zero Punctuation EVE Online Review comment thread, I recommended City of Heroes. I don't know if that spurred him to action (not too likely given the plethora of other ways he might have heard of the game) but hey, I get "I told you so" props for City of Heroes not being immediately terrible, don't I?
From the Game Damage review, it seems Yahtzee's main turnoff of the game right now is that they seem to be running some kind of game event that has zombies spawning in newbie zones. (It's a little ironic considering that, while it's quite disorienting to the new users, dynamic content (even crudely forced in a temporary event) is quite refreshing for established players.)
That said, I'm currently really burnt from City of Heroes and am anxiously awaiting Champions Online, which will be true a City of Heroes re-designed sequel in every way but intellectual property.