Playing through Fallout 3 at the moment for the first time. It's okay, don't get me wrong. But I detest first person shooters, aiming never feels natural to me when I'm playing them. So I'm going the stealth/melee route with my character - and man, does this game punish you if you get caught trying to backstab.
That's another thing, at least Oblivion handled the stealth aspect well - Fallout 3 relies far too heavily on it's gunplay. Plus there's also the mini-map, the lack of good dialogue choices in conversations and the general brown 'n' gray colour scheme.
Also... and this might get me some flames... Half Life. I did not care for Half Life. It's in fact part of the reason why FPS's turn me off so much. God knows I tried to like it but it just seemed like nothing special to me.
Both probably really good games if you like that sort of thing. To each their own, I guess.
One further note... I loved Bioshock, just in case you think I wrangle all FPS games into the same camp.