Yea get HL2. I got it the day it came out last year, the first time thru it is amazing, especially since at that day i never saw a computer game like it. But going thru it more then once or twice got kind of old personally, that's just because I have alot more games now. But for me to be able to play a game all the way thru more then once isn't very likely in the first place.
Get Quake4 if you like muliplayer FPS. The actual story is kinda lame and repeditive. I whent thru it way too fast. F.E.A.R from what i've played, (the demo), was fun.
I'd still suggest Doom3 even though it's now kinda older, I loved it.
BF 2142 looks freaking badass. I can't wait to get my hands on it.