Try working more visual interest into the textures, since it's a zombie game I suggest getting really grungy with it; rust, dents, grime, and blood. Use every opportunity to emphasise details and volume, highlight edges, drop shadows, etc. This kind of stuff can really help the readability of the model, and get it to kind of pop out from the environment, sort of like outlining and rim highlighting can with 2D sprites in 2D games (note the bottom of the machine and the left edge in my render).
The front face of the machine could really use a lot more work. I played a little with it, mainly adjusting composition, adding an actual vending machine interface to it and rendering the pistol.
Compact your texture! You're wasting a lot of space in your image. Also, I don't think you even need to have a bottom face on the vending machine at all. Is it even actually possible for the player to ever see it? If not, it's a waste of polygons and texture space to include it.
Uh, forgive my horrible render. I have little knowledge on 3D programs myself
EDIT: Fixed the render
