From my own work in 3D, I can tell, first of all, this isn't true 3D, at least what I think of as 3D. Because it is simply a 2D plane in perspective, it would probably be very hard to create a map with more than one story. It would be possible, but very hard to do.
Also, I noticed that the orange trees were always drawn on top, even when green trees should have been in front. I would assume that you are using this trick to maintain the framerate, but it would utterly fail if you decided to use anything besides a monochromatic (meaning without a gradient or another color) color scheme. Actually, regardless of that, you wouldn't really be able to track bullets with the system you have here.
It's a good start, all things considered, but it would probably be somewhat useless as a kit because you are missing some key features that are necessary for FPS, but probably too hard for most Stencylers to figure out.