I like the assassin's creed multi player option. We can all assassinate each other. Watch out I especially love jumping off of roof tops and landing on people with my blades.
There are a few different modes in multi player.
Manhunt: You and your group of 3 other players hunt down another team of four other players. At half-time, you switch sides, and you have to hide from the enemies, as they are now tracking you down. (I call this hide and go kill)
Wolfpack: Pretty much the same as Manhunt, except you're always hunting the other players, but they are NPCs, and you work with 3 other people to kill them as you try to reach the final Round (Round 25).
There are a few other modes...