Thank you for the footage! Did you find any issues in the Linux build? I saw a couple visual ones, but I'd be interested in knowing if the level/dungeon editors saving/loading works.
You can exit upgrade stages without spending money, the doors are always open, but in the next build the door opening animation will be delayed (I didn't intend for it to be hidden by the screen transition) so hopefully it will be noticeable.
Regarding bullets, they bounce halfway up the wall. The perspective is angled so that the side of a wall will have the same vertical pixelcount on screen as the top of a tile, so you can base your measurements off of that. Basically this means there's half a tile more "inside" the upper parts of walls, and half a tile more on their visible side. For enemies and the player, the hitbox is more "what you can see" rather than x-above-from-the-ground-accurate-in-3d.