Team Fortress 2:
Right off the bat, TF2 distinguishes itself by its different and in many respects, daring visual design style. Each of the nine classes stands competely distinguishable from any given distance due to the drastically unique profiles and brightly highlighted color schemes. TF2's "Pixar-like" graphics make the game immediately feel like a cartoon, its vintage feeling and old-timey map introductions give the impression of an over the top 1960's spy film, and its fast paced, team driven gameplay lets skeptics know: Team Fortress 2 is not a game for babies.
The game originally launched with 2 different game types: Capture the Flag and Control Points. And since late April, Valve has released a game mode known as payload, all of which can be explained in all of the hundreds of articles written on the game. The important thing that needs be said is this: while at first glance TF2's limited number of gametypes and set of about 8 Valve created maps may seem barebones, the experience almost never seems dull, repetitive or lacking.
Valve went above and beyond when it came to balancing each of the nine playable classes. Each class has its stated purposes or play styles (Offense, Defense, or Support), but each class, when played in the right hands, can be used for practically any job. Every class can be defeated at the hands of any other if played correctly, which makes for a continuously challenging and fun play that almost never suffers from teams full of all soldiers or demomen.
Speaking of classes, each has its very own unique and completely different playstyle. For those who prefer the "run and gun" kind of play, the Scout would be a good choice. Those who like to play sneak and ambush might check into the Pyro or Spy. Soldiers and Demomen might be good choices for anyone feeling particularly destructive. The list goes on and on, but needless to say, anyone could find a class to play.
The name of the game is TEAM Fortress 2, and rightly so. This is a title for those who like the idea of working on a team to achieve an objective, not to see who can "pwn the most n00bs." While particularly skilled individuals may shine, if the team fails, EVERYONE fails (and most are promptly mercy killed as payment).The game supports a multitude of in-game chat options for team communication and coordination, but if you want to really get the most out of the experience, voice communication is a must. The game has decently reliable in-game voice support, which makes coordinating and making on the fly tactical decisions easy and rewarding. The game encourages, nay, demands being able to switch strategies on the go, with the ability to switch classes between respawns and multiple paths to any given objective.
On top of all of that, Valve is consistently making patches and updates to both fix any bugs, exploits, or hacks discovered in the community as well as to add new content such as maps, gametypes, and class achievements and alternate weapons. In addition, Valve takes the time to personally reply to and address any issues brought to its attention. All of this together makes for a customer service that outdoes any seen by practically any other game developer.
As with any decent team-based games, the team you have can make or break any given experience. There are literally thousands of TF2 servers out there (its a game running on the source engine, so of course there are), many with various and ridiculous mods a la Counter-strike. But put in just a few minutes of searching (maybe a Google search here and there) and you'll be able to find plenty of reliable, fun servers full of rational, skilled players that make for an irreplaceable experience. There's nothing like having a back and forth match, seeing your team beaten back to its last control point then somehow punching through and retaking ground. Having a team of other players that can respond and coordinate better than any "bots" ever could is something that TF2 takes full, bloody giblet-filled advantage of.