I love the concept and how fluid everything feels. I really like the way the level design punishes you for getting every molecule you see, making you get stuck in tight spaces; it's like it is telling you to be mindful about when and how you need to grow. I don't think the levels are that hard, instead you just need to try new things until you find a good route. However, I also think that a couple of build-up levels would be great.
The art style is very clear and charismatic. Somehow the cells and the bacteria look cute and funny.
Nice work!