TwoGuns Suggestions:
Weapons:
-Flamethrower
-Minigun
-Some sort of sniper
Maps:
-Bedroom port for luls
-TDM map
Gamemodes
-TDM
-Deathmatch
Misc.
-Gore mod
-Playertypes? Not sure if it's possible.
-Support for vehicles? Again, not sure if it's possible.
In fact, I don't know how easily you can mod this game, but hey, they're ideas.