Left 4 Dead 2

There is one game I will never get sick of playing online and that is Left 4 Dead 2. The L4D series is your typical zombie killing survival game. Don't get hit by zombies, fight your way through them, and get to the next safe room. With this game, you have four survivors, Coach, Rochelle, Nick, and (my favorite) Ellis.
When you play online, there are a couple game modes. Right now, I'll tell you about versus, which is the best one and most played.
In versus, you play the same as single player, but you have other players as your survivor counterparts. The object is to work together as a team to get to the next safe house without dying. The catch is, there is another team of four players, but they play as infected. In L4D there are special mutated zombies with their own abilities. There is a boomer who will emit boomer bile on you which limits the survivor's vision and attracts a horde of zombies. The spitter spits acid which will injure survivors the longer they stand in it. The smoker has a very long tongue that can grab a survivor and take them away from their team. The hunter probably does the most damage if a survivor wanders away from their team. The hunter pounces onto a survivor and "tears" and scratches at them. (This is really not a game meant for kids who are not at least a teenager age.) Finally, the Tank is a special mutated super zombie that can only be controlled a certain amount of time by someone on the infected side of the online play. The tank is huge and can hit very powerful hits and pick up pavement and throw it at the survivors.
The winner is determined by who has the points at the end of the game. Since the two teams take turns being the infected and survivors, the points add up by how fast they got through the level, how many hits the infected got on the survivors, and if any of the survivors were killed, points are deducted or just not earned.
I find this game to be one of the more fun games to play online because if you get a good team together and you're against
a good team, it adds for a challenge.