Look at this tiny naked dude defending the furnace! What a guy!
Normally I'm not a huge fan of pixel art, but I think it really works here, with the retro sound effects.
Gameplay wise... I liked your game, but the furthest I got was the third wave! But even at this point I've seen a nice variety of upgrades, weapons and mechanics!
I'd say your submission plays and looks pretty good, but there's one more thing. I can't really see how the game relates to the theme. Like... you are already there! There's no way home, and if you leave the immediate vicinity of the furnace, the way back is a short one!
Over all- good submission, but I'd focus on the theme more next time. Keep it up!