I have FEAR, but I never liked it too much.  It's just not as impressive as some of the other shooters out there right now.

You could get Warceaft 3. Not for the game itself, but for the excellent mods.

Is COD4 really better than CS:S? I heard there was quite a few amount of luck involved in COD4(which would automatically put it below Counter-Strike), and not as much skill. But I can't comment on it, I only played COD4 a bit and never played CS:S. 

As for FPS with classes, Quake Wars: Enemy Territory is far deeper than TF2. You don't even need to kill in QW:ET to be useful (this applies to every class except Soldier/Aggressor).

@Deegan: Try RTCW: Enemy Territory, it's free and it's really good. After you tried it, if you want a deeper Enemy Territory, you can buy the retail version 'Quake Wars: Enemy Territory' for only $20 on Steam or Retail.

I hate how people assume if a shooter has a FEW random elements, like straying bullets or whatever, that it's automatically not fun.

Sure, if you're earning big bucks in huge tournaments, maybe you're better off sticking to CS 1.6.

For the rest of us, we'll play a fun game that still takes a good amount of skill to master.

There's very little luck other than airstrikes, and you only get those if you were good enough to get kills without dying in the first place.  The air strikes add a lot of chaos to the game and it keeps it fun.   Most of CoD4 is pure skill.

Quake Wars is more complex than TF2. That doesn't make it deeper.  It has nowhere near the balance the TF2 classes have.   

Battlefield 2

Because this game is from 2005 its pretty cheap now, at least here in the USA it is.

Decent video review can be watched here (remember this review is from 2005, you don't need todays top of the line card to really enjoy it):
http://www.gametrailers.com/player/6916.html

I've played this for over 1300 hours since Jan. 29, 2006

@naznatips: The classes in Quake Wars:ET are extremely balanced. I would go as far as say that it has the most balanced classes I've ever seen in a game. More balanced classes than Diablo 2, WoW, Guild Wars, Battlefield 2, RTCW:ET, etc...

The only balance problem in Quake Wars is that the Strogg side is slightly stronger than the GDF, though I prefer playing GDF.

Warcraft 3 I would recommand starcraft but it is to old. Enemy Territory is also a god game.

you can plar Tales of Pirates or Sword of the New World. They are great MMORPG

Multi FPSs that have the most players in no specific order
CS 1.6
CS:S
TF2
CoD4
BF2

Am I missing anything?
All of em have different gameplay but are good games, hence the big # of players online.