Action Packed Party
Team Fortress 2 fits for everyone.
So yeah, there's a lot of cartoon gore, bodies blow up in a blood filled explosions and it may not be suitable for the lower ages (though you may find 8 year olds playing it and cussing severly), but mainly this game is for everyone.
While playing the game, anyone can find his own gameplay style and favorite class, While I prefer Pyro and Medic, you might excell at being a spy, or soldier or any of the classes.
As the game offers, the game indeed has unique gameplay for each of the nine classes- Engineer (which builds teleports, sentry guns, and dispensers), Demoman (Plants stickies, which are Pipe bombs that attach to walls and ceilings, and also shoots grenades), Heavy (Uses Mini-gun and basically the most powerfull class In-game, but very slow), Spy (Uses disguises and invisibillity to infilitrate enemy lines and backstab/sap their Engineer structures), Pyro (Burns, Burns, Burns), Soldier (Uses rocket-jumps and basically blows up stuff), Scout (Extremely fast and used to capture Intel, which is the flag, and capture points), Medic (Heals stuff and has a special ability to go invincible plus another team member for couple of seconds), and Sniper (Bewm Headshot).
Several game modes are included, the classic CTF (Capture The Flag), CP (Capture points), and Payload which is a game mode in which you drag a cart, and the red team has to stop it.
The game also has achievement system (At the time of writing only two, Pyro and medic) that earns the happy achievers new weapons for their class.
All this is nice and good, but there's only one way in which your team will win, and it's co-operation, if you won't listen and go solo, it'll be lot harder for you, but of course, some can manage by doing that also.
to sum it up, if you like online co-operation and humor, TF2 is the best choice for you.