The "go up a level" tiles could stand to be more visible. It took me a while to clue in to what they were... Maybe make the little box on the wall glow blue or something?
I am also stuck.
I have the left gun module, but no gun for it. I put two fuses in the control unit; it doesn't seem to do anything. I can select cracked walls, but can't destroy them. All I can seem to do in the upper-right unmarked mine is rapidly deplete my credits trying to get to what appear to be three health bars. I have checked all of the storage boxes that I can find in the lower mine entrance (even the one behind the three enemy bots). If the way across the lava is "straightforward", I guess I am just not a straightforward thinker, lol ¯\_(ツ)_/¯