What sort of system did you have in mind for the aiming and/or weapons?
the player will always stick to a trusty revolver. however, there will be a BUNCH of different ammo types to range from.
there will be incendiary bullets, plasma, freeze, lightning, arrows, etc. but will always be shot at the pace of a 6 bullet revolver. the default bullets will have unlimited ammo but for the other ones you'll have to search and collect them.
also as for the aiming you'll be aiming with the arrow keys. besides aiming sideways, you can aim up and down when you're in the air.