I absolutely love the aesthetics of this game. The art is incredible and it all moves and sounds great.
The deliberate "slow and heavy" moveset is interesting but I don't think it works as is. The slow movement discourages the exploration that is core to a metroidvania, though the presence of a sprint upgrade later on probably mitigates that (I didn't reach this part). My biggest issue was the fixed-length jump. I'm not against the idea in theory but I think the metrics should be stricter for it to work, almost built on a grid. Like in the room where you get the attack upgrade, if you stand in the middle of one platform before jumping, you will miss the next one. At first the jump seems to connect but then your character keeps sliding somewhat and fall off the platform, which is incredibly frustrating. There's many such occurrences where it feels like the environment wasn't really made to accommodate the jump length.
And the final issue is the lack of checkpoints. If the platforming is going to be like a puzzle to solve, then almost every platform should be a checkpoint. Being sent back to the attack upgrade room every time I missed a jump in my way back to the main building was discouraging. This checkpointing would have worked in a game with fast movement, but here the slowness makes it very tedious and punishing.
But fix those two issues and I believe you will have a very interesting and fantastic-looking game. Good luck! ;)