Better than Halo and Counter-Strike. The Best Online FPS Ever.
There are huge differences between CS and TF2 (aside from TF2 being leaps and bounds better than CS). Number one is the art style. The cartoonish look is so beautiful, and it won't take too much horsepower from the gaming PC to run this either. Number two is the class based system. So, TF2 has 9 different classes, each one wielding different weapons and each having a role that each needs to follow if you would like your team to be successful. All the obvious classes are here, the mostly up close damage classes (Scout, Solider, Pyro, Demoman), the big but slow class (Heavy), the one the makes things (Engineer), the healer (Medic), the stealthy class (Spy), and the long range d class (Sniper). Oh, and if you want another reason that they're different: Team Fortress 2 has no 'nades.
The balancing is near perfect too, you'll probably learn and love to play each class really quickly, though some, such as the Spy, are much more harder to be able to be dominate as, but for the most part even the casual players will have fun here, if not, they can still just admire the look of the game.
The game comes with 4 game modes, playable on six different maps, not counting the new modes and maps from consistent updates that Valve has released (and will be released). All of the maps are incredibly designed and phenomonal, so you probably won't find yourself playing on any of those "unofficial-and-usually-bad-community-maps." Luckily, Valve let's you easily filter the official maps from the user made maps. Anyway, the modes of the game are Capture the Flag, Capture Point, Arena, and Payload. The modes are hardly anything new or special, but they're still fun as hell. Capture the Flag doesn't need to be explained, you just capture the intelligence from the other teams base and bring it back to yours. Arena, which is, more or less, a team deathmatch where you don't respawn. You win by capturing the point in the middle or killing everyone on the opposing team. Capture Point has you capturing all of the points on the map by standing near them with your teammates, again, nothing new. And Payload, which is the most innovative mode of them all, which has you pushing a cart to the other teams base, and the cart is full of explosives, so when you reach their base... you guessed it... BOOM! It blows up.
TF2's 9 years of development were obviously used well, because Valve managed to create, along with Blizzard's World of Warcraft, a game that I've become completely addicted to. It's hard to put it down. I really do believe that this is the greatest and most complete multiplayer experience ever created, period. Not to mention it comes in a great collection of games in The Orange Box.