For those who don't know, Team Fortress 2 is an online, class based FPS, and a damn good one. This is my favourite multiplayer in an online shooter, for quite a few reasons. I'll go through them now:
1. It's fun.
The simplest reason. The gameplay is addictive and varied, unlike Call of Duty. The game has quite a good sense of humour about itself (with all the funny little one-liners, and the ridiculous amounts of blood and gore), and is quite light-hearted. It always provides a good challenge, just when you think you're dominating the team, your enemy class will own you like a Japanese business man with a mysterious woman in an alleyway.
2. It's balanced.
The game is more balanced than completing yet another see-saw puzzle in Half-Life 2. Each class has particular strengths and weaknesses, so you can't just pick one class and own everybody. This is a massive problem with Call of Duty, as you unlock a gun later on that might as well win the bloody game for you. Anyway, I'll put this in an example: Say you're a spy, you can turn invisible and disguise yourselves as enemies, which puts you at an advantage to kill snipers, who you can just sneak up on and make a new ventilation hole in his back. However, you are not so versatile that you own every class, come face to face with a Pyro and you're going to be made into French Fries faster than you can say "Sacre Bleu!".
3. There's a class for everyone.
No matter what type of shooter gamer you are, there's a class for you. If you just like to stand there with your finger on the trigger until your enemies resemble something that belongs in a soup can, you play the Heavy, if you like stealth and sneaking, like the prick that you are, you play the Spy. It's basically the game equivilent of a schizophrenic sitting in a padded room talking to himself.
4. It's funny.
The characters crack me up more than a sledge hammer meeting fine china. The Meet the Team videos are hilarious (They're goin' have ta glue you back togetha'... IN HELL!"), and the in-game one liners catch me off guard all the time, like when the Spy puts on a Texan accent when he dominates an Engineer, or when the Sniper shouts "THANKS FOR STANDING STILL, WANKA". There's really not much to say about how funny it is, other than YOU ARE ALL WEAK, YOU ARE ALL BLEEDERS.
To summarise, this is one great game, that just missed out on a Top 10 Games of the Decade spot. It's a Valve game, so it supports my argument that they are the best game developers of all time. Call of Duty, bow down to your superior.