If you're going to have death respawn you back in the same room, you need to make it not take your items. The game seems basically unbeatable in its current state - I died in the first room after getting the final artifact and had both the artifact and the key to the final room disappear and I have no interest in getting them back, if that's even possible which other comments suggest it might not even be. Don't understand how this wasn't caught as it seems like an inherent and massive flaw in how the respawn system currently works.
The game was pretty fun up until that point. I liked the gimmick of collecting different items with both positive and negative side effects, but that gimmick completely disappeared in the back half of the game which was really disappointing. I also don't think it really counts as a metroidvania - you never actually gain any permanent abilities over the course of the game, and in spite of its ostensibly interconnected format in practice the world is just a linear sequence of discrete stages.
I encountered a bug at one point where, after dying and losing a key in the green area, I tried to turn around and reenter the previous room to try to retrieve the key from that side, but instead it just took me right to the next area despite clearly entering the wrong door? I think that transition might not be set up correctly, though it did save me a lot of pain with that key.
Hitboxes were also really frustrating especially in that final room. I'd be standing directly on spikes without taking damage one moment and then the next one of the fireball things would hit me while there was a visible three pixel gap between us. The movement cycles of said fireballs also felt like they were aligned in an extremely tedious way that regularly required just sitting and waiting.
The visuals are really nice, you did a good job creating something appealing within the technical limitations. The music was also mostly pretty nice, though I found the final room's song to be really grating after only a few tries. All of the others worked great, just that one needed a little more to it I think.