I only made it to the third level until the game glitched and I was unable to continue.
The concept is good, but I feel the execution could be improved a lot. There are a lot of smaller bugs such as getting stuck inside an opening in the first level if you possess into it, hit detection being a little wonky, and player movement not feeling quite satisfying.
I'm aware that you said that you made a lot of improvements since this was posted, and I'm happy to hear that you're still working on ironing it out.
I genuinely like the idea of possessing different enemies in order to progress through the level, but I ultimately didn't find the mechanic to be necessary for no other reason than additional health. I think if you create puzzles that require you to be a specific enemy, it would be more interesting.
Onto a more specific detail, I didn't feel that possessing into the projectiles to reflect them was a worthwhile idea. You get pushed too far back that you'll essentially go backwards, and the projectiles don't harm the enemies.
I think you can turn the idea into something really good- but the project needs a lot of work. Of course- this is not meant as an insult. I think once you can create good puzzles, iron out the bugs, and refine the player movement to feel more responsive yet smooth, I think the game will begin to take shape.
Take care and thanks for allowing me to play it and give my thoughts!