I was worried that would happen with the title - I didn't have a chance to test it under multiple screen resolutions (it should display properly at 2560x1440). I just ran a quick test at 1080p and the actual game seems to display correctly (looks like the issue is with the GUI layer and the 3d camera appears to be tolerant to varying screen resolutions - I guess that's what I get for using magic numbers on that). You figured out the issue with the hit sound! Looking at the source code, I only call the audio clip on the horizontal collision and forgot to add it to the vertical collision. Enemy AI is super basic - they just kind of point at the player and go (the clipping issue with the boss and walls is because I forgot scale the hitbox up with sprite, so bosses have the exact same hitbox as the regular enemies). If I come back to this, I'd like to add some real pathfinding and a real attack state (right now the player actually takes damage in the player collision code and that's why the enemies don't damage the player if you stand still).
The enemies actually have a 10% chance to drop batteries on death - if you run enough trials, you can see that every once and a while health will get restored. The batteries were one of the last things I coded before submitting and I think the graphic for them is getting drawn somewhere out in space for some reason. The shift key thing is that at one point I played around with a time slowing mechanic and when I abandoned it I must've missed commenting it out in a few places.
There were a few things that I had planned to add before I ran out of time. I wanted there to be doors that didn't open until all the enemies were cleared from a room, I wanted bombs (and like treasure rooms you could bomb into), I wanted the walls/floors to have multiple textures that would be picked randomly (like the bricks could have multiple levels of distress or something - just something to break up all the same-ness), and the big mechanic that I wanted to add would've been a shop/inventory system where you would've been able to upgrade body parts of your robot (like stronger arms/different weapons, faster legs/wheels, maybe limited use items like stealth/smart bombs) - I never got far enough into that to decide if there was going to be like a currency or if it was going to be an experience/skill point kind of thing (maybe a little of both?).
Thanks for the comment! You helped me track down at least one bug that I hadn't figured out yet!