Ok, first things first... this game has amazing art! I love the animation, characters, background art... it all looks great! There's a little visual glitching, but it's not too bad.
I'm impressed with the huge amount of content as well! Tons of enemies, upgrades, a large map, multiple bosses... all really cool! The theme interpretation is good, and the story, while not huge, gets the job done!
I love the different abilities that you unlock as you play, gives that great Metroidvania feel. They're all useful and cool to start using.
The audio is fine, I like that there's music during the bosses. Wish there was some through the whole game.
I do have a few critiques. First, the combat feels a little lacking, for lack of a better word. Maybe a little more impact or weight. Some sort of reaction from the enemies, or particles blasting off. It felt hard to avoid damage in a lot of situations, so I often just tanked while slamming the attack button. Since you can't stay dead, it's not a huge issue.
Second, the spikes... those would drive me nuts. Especially when you have to start climbing, jumping, dashing, bouncing all around them. It felt more frustrating that fun at times. The lag after getting hit started to grate on me after awhile. I also had some weird glitches there. It was near the second boss room, after hitting spikes I'd often start... floating? I'd lose the ability to use actions, but could float around with the arrow keys. At one point this lead to a full crash, but thankfully my save was fine after refreshing the page.
My final critique, and take this one with a grain of salt, because maybe it's just too much for me... but that final boss. I found it really frustrating. The hit box of the boss seemed odd at times, the narrow little spaces to jump/dash through. While I understood what to do, felt a bit too touchy/difficult for me. I gave it a good 10-15 tries before giving up. I was able to reach the "red-eye" stage twice, so I feel like I was getting close, but without a health bar it was tough to feel like I was making progress. Another thing that might help there is adding a save point right before the boss. Going back to the base isn't so far at first, but after the 10th time of going through the door, down the elevator, it adds up. Assuming my save-file holds up, maybe I'll give it another shot later, but there are a lot of other games I need to try first! (One other note, I had the attack +1 chip, attack speed up, and 1 upgrade on the weapon. Maybe there's a better chip combo? I didn't farm enough atom to get all the chips...)
Anyway, critiques aside, this is definitely one of the best entries! Awesome work!