Really fun game with loads of content. I've enjoyed this game every time I've played it, even though I've beat it 6 times. I'm not gonna lie though, it's still a really hard game and takes a lotta luck to beat.

TF2 is easily one of if not the best games I've ever played. It has such unique characters and is amazingly well balanced. All of the different weapons promote different play styles allowing people to decide how they want to play the game.

There's also the (obvious) promotion of teamwork that really makes this game stand out. The visual style is amazing as well. It may not be "realistic," but I'd personally prefer TF2's graphics over realistic graphics any day.
Another thing about TF2 is the unique game modes. Each one promotes different play styles and strategies for victory that always keep this game from getting boring.

Of course, I still haven't mentioned how involved the developers are with the community. From the community created maps that have become official, to community created weapons and hats (which all allow the creator to earn a share of the profit)

And the best part is, all of this can be yours for the amazing price of free, so there isn't a reason not to get it.