The Bottom Line:

"Best in series"

Don't convince yourselves that the game is old now, and sucks for being old! It's unfortunately a mistake I see many people do and it isn't supposed to! This game is better than many new FPS genre I've seen lately.
It's so complete in the combat, weapons, characters, game modes, everything!
It's just complete fun and it's a game you can always "return" to, you never get tired of it after all this years, I know I haven't.
Not to mention the multiplayer game mode, that is tremendous fun when your playing with other people Online/LAN, etc...
As for the maps, they are all incredible, they are so well structured with the game modes and fit so well.
This goes for the characters aswell as for the weapons, that are so original and fun. You can personalize your own character.
The interaction with the maps is great, this game is very revolutionary and in my opinion makes way to the new wave of new FPS genre games.

I recommend this game for everyone! Specially people who like FPS, blood and gore and just plain fun!

Try it! This one should be mandatory on all PC gamers!