How about (given that you want to use 3dgs),
you make a sideview Shooter using 3D Models.
So it looks and plays like the old 2d shooter games, but
uses 3d Models.
A similar approach was used for Street Fighter
http://www.youtube.com/watch?v=JWIPJS6qB...=PL&index=6or this Unreal Tounament "2d" mod
http://www.youtube.com/watch?v=55yxnCFy8m4&feature=PlayList&p=20E57D6CCEC7D66F&index=0
