nice work.What you did is a very common Beginner error. make round parts look round. In 3d Software you can smooth surfaces. each surface can store info about it light properties. so you can set it that every face shows the light back in there own normal direction or smooth many faces to a soft surface. "Smooth" is the magic word you need to search for. With this surface smoothing you can create a 4 sided Cylinder and let it look round. (as long as you cant see its end)
With this knowledge you can reduce a lot of polys. the gunmask for example, you can delete every 2nd edge and it will look the same. same for the barrel holder it can have 4-6 sides and will look perfect round. you can that for everything. the Coaxial MG mask.(could be reduced by 75% imo) The Barrel front can use more polys as the end, where it meets the gunmask. Also the second Row of wheels can use less faces as the front wheel because they are hard to see.
same for the wheels you can do some tricks to let them look more round. 16-18 sides is more then enough. you can use Alphatextures. Fh2 do that a lot. the advantage is that you only need 2 faces to produce a PERFECT round wheel ;)you can also use a 16 sided cylinder and paint your Texture round on it. nobody will see that its not round because the eye will ee the texture more as the surface. (check out older games the did that often)
http://wiki.blender.org/index.php/Doc:Tutorials/Textures/Use_Alpha_for_Object_Transparencyi can see that you have many unneeded verts too. from parts where you extruded the "turret"
try to optimize as much as possible. and aim for around ~ 8000 Faces overall with tools, bagage etc.
Good work keep it up.
