Looks nice and plays pretty well, though the jumping sometimes gets locked for some reason.
A lot of the sounds feel very out of place. The first one that comes to mind is the sound effect for your main gun. Since I'm controlling a big stonking mech I expect a satisfyingly meaty cannon/rifle sound from it, but instead it sounds like I'm firing a dinky pew pew laser gun. The enemy soldiers on foot have meatier sounds for their guns.
I also noticed you re-used the sound effect for the players gun for some enemies guns (don't remember which). I'd suggest avoiding that because it can be slightly confusing.
Talking about audio, some more varied music tracks would help a lot. The first level has a very much ambient track. Which is good, helps set the mood. But for situations like the truck sequence, something more energetic will help a lot to engage the player.
Btw, that text screen just before the truck sequence, way too much text to set up such a simple scene.
You could also give some more feedback to the player. For instance, the first time I ran into the drone spawners (or whatever you call them) I didn't know if they were destroyed when their sprites changed. The broken state wasn't drastically different from the normal one so at first it looked like it was partially destroyed.
You have to duck to be able to fire on the regular soldier enemies. This would be fine if I could just tromp over them instead of shooting them.
You also have some wonky english here and there.
Anyway, looks to be a cool game.
Edit: I figured I'd go back and double check some things in the game, but I'm currently stuck on the loading screen.