At the time of this writing I've spent around 20 hours playing this game and honestly the game is pretty addictive once you get into it. There are 9 classes or roles to choose from, each having their own pro's and con's.
The scout is fast and agile, yet can sustain very little damage. He is equipped with a baseball bat, shotgun, and pistol. The scout also has the ability to double jump in the air. His speed make him useful for getting to points on the battlefield quickly. The soldier carries a shovel, shotgun and rocket launcher and has the ability to shoot a rocket at his feet in order to jump higher. The soldier is effective at both offense and defense, your unit of choice for many people just starting the game. My personal favorite is next, the Pyro. The Pyro is equipped with a flamethrower that will cause damage to another player over time as they burn, so even if you kill the pyro assaulting you, you may already be dead. They also come with a shotgun and axe, and the shotgun can be switched with an unlockable flare gun that will set people on fire. The Pyro also has the ability to deflect projectiles with their compression blast, allowing them to clear the path of sticky grenades.
Speaking of sticky grenades, the Demoman is the one that unleashes this weapon. Equiped with a grenade launcher and sticky grenade launcher, as well as a jug of some sort, the Demoman can send explosives hurling toward the enemy. The sticky grenades are a lot of fun, placing them in just the right spots and blowing them up at the right moment can turn battles and get you a lot of points. Heavies are large characters equipped with miniguns, shotguns, and fists. They're pretty slow but make up for that in firepower. When teamed up with a medic in the right situation, the Heavy can dominate an area and repulse an enemy assault. The Engineer is the last "defensive" class. Equipped with a pistol, a wrench, and can build teleporters, sentry guns, and health dispensers. The engineer can shore up any defense with well placed sentry guns. A well placed sentry gun can stop a whole team in it's tracks long enough for your team to win the game. I have to say, those sentry guns are vicious on most payload maps.
The Medic is the healer of the battlefield, keeping teammates in good health with his medigun. He can also deploy an "Ubercharge" that will make the medic and the person he is healing invincible for a short period of time. But don't think Medics are defenseless, they are also equipped with bone saws and syringe guns that can make any overanxious enemy reconsider attacking a medic. The Sniper is another self explanatory class, equipped with a sniper rifle, SMG, and large knife, the Sniper is the sharpshooter of the team, taking enemies out at extreme range. Heavies should avoid going into the open if snipers are present, but if you manage to get in close with one, you should come out the better. The sniper rifle also charges the longer it is in zoom, allowing the sniper to get a more powerful shot off. Finally there is the Spy, equipped with a revolver, a knife, and electro sapper. The Spy can disguise himself as a class on the other team, allowing them to slip in the back and preform "backstabs" and "sapping" enemy engineer's constructions. Backstabs involve stabbing an enemy player in the back, while sapping is putting an electro sapper on an enemy dispenser or sentry emplacement in order to drain power and health from it, causing it's destruction. However, once the spy uses his revolver or knife, he is instantly uncloaked. It is always better to kill the engineer before placing electro sappers on the sentry gun and other buildings.
What is cool about these characters is they all have different strategies and even come from different locations on the globe. The Medic is German, Sniper is Australian, Demoman Scottish, etc. Gives the game a little bit of atmosphere.
There are several gametypes, control point (cp), payload (pl) and capture the flag (ctf). In control point mode you attempt to capture control points in a tug of war type style. Generally there is one neutral point at the start of the game with both sides other points locked. Once the middle is captured by a side the other team's next control point is unlocked allowing for capture, and so on until all CPs are captured. Another version is a offense/defense type in which one team attempts to capture 2 control points, 1 at a time, while the other team attempts to stop them. These game types are probably my 2nd favorite out of the three.
In Payload, the blue team is charged with pushing a cart from one side of the map to another along a track. How fast the cart moves is tied to how many players are pushing the cart. "Pushing" is basically standing near the cart, you can still fire your weapons and everything. The Red team is tasked with stopping the cart before it reaches its final destination. If the players pushing the cart are killed, the cart stops and after 20 seconds begins to move backwards slowly. It will only stop moving backward when the blue team pushes it again. Honestly this is my favorite game type. There are so many things going on, trying to gain the upper hand so that the cart gets to where it needs to go, and many times it devolves into a massive melee of people attempting to defend the cart or push it farther. This is the most exciting part. Its kill or be killed at it's finest.
Lastly there is the classic Capture The Flag, but instead of a flag it is a briefcase with important documents in it. Once the case is stolen it leaves behind a trail of papers that can help the hunt to find the person holding the case. This is my least favorite but still a lot of fun. It just doesn't have that wild "anything can happen" feel about it that the other two gametypes do.
Factor in the ease of learning the game, cartoonish, yet wonderfully done, graphics and general fun and this game is one of the best Multiplayer FPS games out there on the market today, which is why I give it a 9.5 out of 10.