The graphics and music are amazing, and worthy of great merit on their own! I loved the diverse critters, and especially liked the silverfish things, which were a really unique and memorable enemy.
Unfortunately though, the gameplay had some problems. Firstly, NEVER put a delay on your main weapon. It feels very clunky to use, and the full second of waiting time just made it hard to land hits. Delays can be good on powerful weapons, to give a sense of build up, but in the game, the delay just feels like a nuisance. Secondly, avoid momentum. This wasn't really a big deal, but momentum makes you feel out of control, like the character is just doing its own thing. Thirdly, take the time to polish hit boxes. Nothing feels more unfair than weird hitboxes, and I'm afraid that the first boss was the tipping point for me. The knife hitbox was mostly over air, instead of the actual sprite. The boss itself had a huge hitbox, especially when it transformed. And the boss teleported around, taking a few health off you without warning.
It's really unfortunate about all of these small issues, because the game looks and sounds great. I didn't have the willpower to beat that boss, the hitboxes and delayed attack were quite frustrating, but it looks like there's a lot more I didn't see. As mentioned earlier, I love how unique the enemies are, there isn't any generic patrolling enemies; they all have their own special behaviour. The music was awesome, I loved the classic touches. I really hope that this feedback is helpful!