Ages ago, I was a runner up for a Quake 2 competition. From then on, my FPS skills have slowly deteriorated compounded by the fact that my interest drifted to the Clie and OS X. Anyway, this summer, I decided to finish one game. I didn't know I would end up finishing three.
For those who know me, I don't use cheats. I hate it when a game's so well designed that it's completely ruined by a god-mode or something. I also played these games on my PC (Pentium 4 1.7, Ti4600)
Anyway, here are the games plus some comments.

1.Call of Duty
I freaked out in this game. I was totally scared of dying during the early levels because I felt I was really there. I hated it when I turned corners only to meet German troops head on. For once, I was really cautious... liberally using anything to hide behind in and to attack from. Graphics and sound were realistically rendered. An exploding grenade and its resulting effects made me observe the situation with awe. This is my favorite game to date and It's probably because the setting is based on real life circumstances that made Call of Duty a not-to-be-missed experience.

2. Halo
I think Call of Duty trained me to be more cautious in this game allowing me to finish some of the tougher levels easily. Halo's level designs are fantastic. They're huge and offer many alternatives to solve a goal. Graphics and sound are well done and it's written well too.

3. Half Life
Half Life is a classic but I never really got to finish it during its time. This is a long, tiring, but exciting game. Each level is huge but a bit linear in design. However, it still manages to offer surprises until the very end. If there's a game that has tempted me to cheat, it's Half Life, where the closest I got to cheating was downloading a saved game file so that I can skip to the level I left off about four years ago.
Thanks to my girlfriend for explaining what "half life" really means.
Images were borrowed from Amazon.