One of the finest multiplayer experiences available
Team Fortress 2 is one of the five games which were included in the excellent package from Valve, The Orange Box. The multiplayer component of the five, Team Fortress 2 is five stars for it's fantastic gameplay, comedic characters and phenomenal level design.
The game's nine classes are very different from each other. So different that each one is like a different game experience entirely. Scout for the twitch players, Engineer for the more tactical minded, Snipers for, well, snipers. And yet, what makes a team successful isn't always the skill of individual players, but how well the team is balanced class wise and teamwork wise. The game isn't called Team Fortress 2 for nothing. So here's the pro and con breakdown.
Pros:
9 entirely different and balanced classes to choose from.
Genuinely funny characters (Ever seen the meet the... videos?)
Fantastic map design that suits the game perfectly
Surprisingly deep gameplay
Unique art style
Generally friendly community, with lots of user created content like maps and skins.
Cons:
No singleplayer to speak of (not even bots)
When teams aren't balanced it isn't much fun as your team repeatedly gets it's ass handed to it repeatedly.
Final Verdict: Buy the game, it's only $20 on it's own, and $40 in the Orange box, which I highly recommend as well.