From what I hear the best is Orange Box or some other PC shooter. My personal favorite is Link's Crossbow Training; although, I hear good things about The House of the Head: Overkill.

Sin & Punishment.
It was released this gen for NA. =P

In this order:

1) Call of Duty 4 (both PS3 and 360 versions are amazing)
2) Left 4 Dead (that game is amazing if you look past the slightly out dated graphics)
3) Bioshock
4) Gears 2
5) Halo 3

Spy Games: Elevator Mission

Call of Duty 4/Call of Duty: World at War (tie) for multiplayer. Bioshock for single player. Nothing else comes close to either in my opinion.

Call of Duty 4

BioShock is not a shooter, so:

1) Killzone 2
2) Gears of War 1/2
3) Call of Duty 4: Modern Warfare
4) Left 4 Dead
5) Halo 3

EDIT: Shit, I forgot Left 4 Dead.

EDIT 2: Counting BioShock,

1) BioShock

2) Killzone 2

3) Gears of War 1/2

4) Call of Duty 4: Modern Warfare

5) Left 4 Dead.

Based on the amount of play time;

1. Uncharted
2. Metal Gear Solid 4
3. Resistance
4. Killzone 2
5. Gears of War 2
6. Gears of War 1
7. Call of Duty 4
8. Resistance 2

At Killzones current pace I will be looking to pass R1 within a day or two. I still have a bit to go to catch up to MGS4, but it will be soon. Uncharted is a differant story. In the end I have no doubt I will play Killzone 2 more than any other game on this list so far. The only way this could be effected is if Konami adds trophies, and eleminates Konami ID from MGS4.

On PC

I have only ever played Fear and Crysis on my PC as far as shooters go,

I'm not a big fan of shooter games but it would be Left 4 Dead, Bioshock, and Uncharted (if that is counted as a shooter).

Not sure about Killzone 2.