Games I recommend
My reccomendation would be - Giants: Citizen Kabuto
This is a favourite of mine. It's very funny and a very different type of fps. Kind of 3 games in one because you can play 3 different characters and stories.
It's quite old now, but was highly acclaimed by all the magazines back when it was relesed, thats what led me to buy it, and i wasnt dissapointed.
Funnily enough it didnt take off with regards to sales, so ide say you could pick it up pretty cheap now.
Quite demanding system spec for its age, so make sure your system is fairly well prepared if you buy it! (800mhz CPU, 32 meg Grphics at least)
Also like Vehementi, I am a fan of Max Payne. Intelligent Storyline, fantastic visuals & Bullet Time feature thrown in for good measure. Almost a perfect game IMHO.