Despite the fact that Shootmania Storm just came out, there's a new game mode and a weapon already available as a free update. "Combo" pits teams of two players against each other who are tasked with killing enemies at the same time -- as you can imagine, a lot of coordination is needed (and probably voice chat).
Evidently, you can switch weapons in this mode, which is a stark contrast to the core game, which forces you to use one weapon at a time. There's also a new weapon type called "the Arrow," which is a ballistic type gun that launches an AOE blast.
Shootmania Storm [Capsule Computers]