There is a free game called Alien Swarm that we used to play the hell out of in college, this is just like it, but in its most primitive form. There is actually a ton of skill involved in covering your partner while crystals get collected for points. Seems like collecting crystals is the best way for points in 2P, one person shooting and one person collecting, then switch when the crystal points roll back over to 100.

Part of the Gotta Run Em All Arcade series - Game #667

Start (Start Pressed) - 01:20

End 50k Points (25k Combined Points) - 04:53

Total 50k Points - 3:33