I wrote down a bunch of bullet points as I was playing. This is from my own perspective as a game developer, so take it as you wish :)
-Very polished experience!
-Music is great and memorable.
-Character animation is nice and smooth
-I think the game is perhaps too forgiving with its coyote jumps, haha. (you can pull off extremely long-distance jumps currently)
-The parallax background is glorious! Also that it's animated.
-Game's first level teaches everything very nicely, however, the first set of spikes can blend a little too much into the background. Maybe they can be more emphasized, or the backdrop could be more contrasted with the spikes?
-I really like the secret maple leaves, it's such an amazing feeling going for them.
-When I'm running, and then stop, the particle effect behind me completely disappears. Maybe the particle system can simply stop emitting while standing still instead, for extra polish.
-The camera is a little bit jittery when the player is on a horizontal-moving platform. There might be something here to experiment with to make it perfect :) (I had vsync off in the settings)
-I couldn't notice the set of spikes at the start of the 2nd level and got injured by them, more than once, haha.
-For the falling platforms after standing on them long enough, consider giving some feedback to player that the platform is going to fall, like the propeller halting its animation.
-Very rarely, when I jump on enemies, it doesn't register. wonder if it's some physics shenanigans.
-I've noticed that some trees are bouncy while others are not. This might end up being a difficult design decision as it doesn't promote game consistency. But it's something that's more subjective so it's up to you :)
-It would be very cool if there's a possibility of playing as the rescued apple.
-This is just my own opinion, but the health bar feels a little high and forgiving. Perhaps there can be less max health but more consistent health pickups. This would result in increased tension but makes health pickups more satisfying to grab.
-I was able to cheese the boss by running ahead of it after hitting its head. Maybe can somehow force the player to lose control while the boss is moving to the other side of the level?
I found only 2 maple leaves per level. So they are definitely hidden well :)
I can see a lot of love was put into it, so really well done for all of the effort. Totally awesome! I'd be interested in keeping up with the game. :)