I like the idea of having experience points by kills
and having some points deducted when a player dies, to avoid crazy kamakazi suicides which ruins the fun
And having specific classes would be awsome, so they have different weapons like Battlefield... I think there sould be more than 3, maybe 6 at least.
DM, TDM, and capture the flag are probably the easiest and best modes...
but it would be awsome to have a capture the territory mode when you get in a gang and get territories like in single player... So whichever gang has the most territory at the end of the game wins.