Haloooo.... ewwww. So bland. The Half-Life series is argued by many to be the best FPS series, but I think it's really just a matter of personal preference. They're all different, so you have to find the one you like the most (even if it's icky Halo ).
It's completely a matter of opinion. But the ones that alvino mentioned are really good. I also like the rainbow six series because they are quite realistic and u need tactics in them.
CS:S all the way man... and wolfenstien was pretty good in it's hey day... btw, nice post alvino... I was gonna post those again, but I was like, why do it again? lol...
I don;t consider BF2 the best game ever. Its a great game and all but hasn't had the impact like CS has had or halo. I figure it'll wear off soon. However I can see FEAR becoming somthing like CS
FEAR is alright... I played the demo and I liked the graphics and the slow-mo came into play, but it's still nothing like Half Life 2 was to me, or even CS:S.