More weapons, more aux weapons, aux shotgun, big shotgun (like sniper cannon or big rocket launcher), aux lasers, FLAK cannon, new enemies(maybe some spiders that can crawl on walls), new aces etc.
New Mech types and modules, like assault, dynamo and maneuver pack imagine some defence pack which makes enemy rockets miss or some flares or antiradar cloak which makes you harder to kill etc.
Weapons with different modes (you press weapon action and it change mode), like shotgun which can change from typical buck shotgun to GRENADE launcher, laser pistol which can transform in enegry sword etc.
I think this game needs more content.