Okay... Let's see this...
Art is very nice, simple, but still looks great. I also really like the submarine idea, it's a really creative way to make a game about exploring underwater.
But man, that was really draining, I'm so sorry :,3
The movement is fine, really, I don't mind it being slow, and I'm glad you had the courage to commit to it, but really, if you're gonna go for slow gameplay, the level design needs to support it. The map is just MASSIVE, when I pressed esc for the first time and saw that yellow dot aaaaaallll the way up to the opposite side of where I was I was legit filled with pure DREAD of having to walk that entire ginormous path. And the fact I knew it was gonna be just a single upgrade and that I would still have to backtrack AGAIN to be able to open stuff right where I already was made matters even worse. Combat is also just non-existant, none of the enemies poses any threat and killing them with the submarine just doesn't feel satisfying at all, wich made me feel like I was just traversing huge chunks of emptiness the entire time.
I also really missed some music here, or at the very least some ambience sounds to be constantly playing on the background instead of every once in a blue moon, because silence really just demotivates me entirely. (I gueeesss silence is more atmospheric?? Idk man, to be really sincere, atmospheric games are just not my thing, like, at all).
Also, the game's resolution simply didn't fit well on my screen, so I couldn't see the lower half of the HUD, and by consequence I also couldn't read any of the dialogues properly
I only played until I got the mines upgrade, and I admit I was already going to stop there, I was already not willing to go any further than that point, but then the upgrade aparently just bugged and didn't work, so that was just the excuse I needed to get out for once. No clue if I was doing anything wrong, the mines just didn't want to come out, wheter I was inside the submarine or not, but oh well.
I'm sorry man, I really really tried to have fun here, but I couldn't think on anything to do for that honestly, I just didn't really wanted to mess around here, so I just got kinda... bored.
But hey, this is still a very impressive entry nonetheless, I admire how you managed to pull out a map this big and filled with good looking visual props in a single month, and as I said, I have huge respects for you diving fully head on on your vision for the game, even if I not enjoyed it at the end. And it's also a complete package, wich already deserves praise by itself.