I actually like the missile launchers, those're nice. You can afford to spend a few more polies though, bevel the edges and stuff at least.
The cannons look awkward and flimsy as hell. They need some meat to 'em. Example.
The texturing is poor overall. The lines of the texture should match the edges of the model as much as possible. You should also texture the missile tubes onto the front of the missile launchers, unless you plan on animating doors onto it, which I'm not sure is possible.