This was actually really intruiging!
I liked that each animal has different abilities and controls - and I liked that they progressively got more challenging. The difficulty curve was pretty good - there was a spike in difficulty for the fish which I think could've been made a little less annoying by allowing us to control the direction to jump, but just when I was about to get bored, the next animal loaded - so the game keeps things fresh at just the right moment without dragging on - a short but tightly designed experience that is of just the right length.
The ending pushed this game up a notch though, I must say that was completely unexpected and very funny. The dialogues that appeared on the screen also sets up the comedic tone and breaks any potential monotonous gameplay by showing you the character's thoughts.
Some improvements I can think of is perhaps the visual elements weren't clear what they were. The pink bars on the first level were supposed to be wallpaper because you're in a house, but I thought it was some part of level design like pink zone = slower speed or something. You eventually learn to ignore it though. Certain household props like the cabinet in the kitchen looked more like they were part of the level too, but they're not. But the table just below it is actually part of the level (collidable). I think there is a lack of distinction between foreground and background. I think having parallax background may help, but I'm not sure. What may also help is reducing colour contrast or using similar colours for the background. That bright pink background makes it stand out a lot more than I think it should.
I appreciated subtle touches like not having me repeat going back through the obstacles after becoming a fly. The fly vibrating, every animal having that distinct yellow hair. Controls were also very intuitive overall. The intro cutscene was also nicely animated and sets the context up perfectly. Also "bag with a substance I prefer not to mention" HAHA.
Overall, this game put a smile on my face, and that's awesome :)