Fun
Actually pretty fun. Eating to grow bigger is a tried and true progression system. I wish it did something novel, but I can't argue that the game was enjoyable.
Aesthetics
The voxel art is really nice, and I would love to the the entire game in this style. The font needs work, the scratch particle system should match the voxel art, and posting text on walls isn't a great look.
The animations are nice.
It definitely seems like a prototype art style. Picking one style would be a good idea.
Music
Music is ok. I wouldn't use it in any finished product. There are better free music assets.
Sound
Bit grating. Especially the mouse squeak. Perhaps lower the volume and pitch.
Mechanics
The movement felt smooth. The hitboxes on attacks need some work.
The growing and eating mechanic was fun. Wasn't a new idea by any means but it seemed well done.
The possession at the start felt unnecessary. It felt like it was added only to make the game fit the theme.
Story
You need to eat to grow, so you can eat the dungeon bosses. Not much of a story otherwise, but it somewhat makes sense.
Theme
Really not a theme here. You are a rat that eats things. It is a bit of a stretch to say this qualifies as "death is only the beginning".
If the possession mechanic was the intended way to meet the theme, more of the game needs to focus on it. Have 10 seconds at the start where you are a ghost isn't a good fit. That's like asking for a taco and only getting a tortilla.