Theme: definitely fits the theme
Fun: the idea of exploring was fun, but what actually happened was I kept getting lost and sometimes I'd be stuck even when I'd explored every area on the map. Never did figure out which things are bombable (maybe there's some sort of visual cue but I didn't see any).
Controls: I like the turn-based/grid-based movement, but the 90 degree turns got really frustrating. Maybe it would help to have keys to actually move left/right in addition to the keys to just turn left/right? Also, the turns were so abrupt/fast it felt a little jarring at times.
Graphics: maybe I didn't get far enough (I got stuck at some point in level 2) or maybe you're using GLES3 and my Macbook Pro just isn't playing nicely with that, but the colors looked a bit monotonous to me (it always looks like that first screenshot (the brown and black one). In this game you do a lot of staring at walls and doors, and I got sick of those walls and doors pretty quickly. I think more variety of colors and textures would help. As jmbjr said, it was sometimes hard to see the minimap, particularly the "you are here" square. Making the map (and the square) a different color (white, maybe), or giving the map a ColorRect so it had a background color (as opposed to a 100% transparent background) would help.
Audio: good ambient sounds, great SFX. I think the game could use some music though. That might make it feel less monotonous.
Originality: the movement system and the swimming to reach areas you couldn't find by walking are not frequently seen; the other stuff is pretty standard dungeon-crawling. To really set this game apart, I would like to see other features that take advantage of the movement system. (For example, I know you worked hard on trying to get a combat system and ran out of time; that would have been interesting to see.)