It's not too hard on its own, no, but it's made unnecessarily difficulty by the checkpoints seemingly not working. I made my way up I want to say most of the tower on level 2, then missed a jump in the section where all 3 platforms disappear at once. I figured okay, whatever, I'll just fall off the side of the map and pick up at the checkpoint I got maybe a minute or two ago. Instead, it reduced my lives by 1 and reloaded the level, resetting me to the bottom of the tower and taking away the tadpoles I'd already gotten. No offense, but I didn't really feel like trying again after that, so I couldn't tell you how the boss fight is.
I think having infinite ammo for the basic weapon is fine for a game like this since it's more about the platforming anyway. Maybe you could give the player other weapons as limited powerups, like 100 shots of rapidfire or explosive shots or whatever's fun. The jumping itself feels fine and the shadow directly below you is a great touch to help you land. Just need to fix those checkpoints so they actually work. Other notes... the take damage sound is kind of aggressive and startled me a little when I first heard it. If you're planning on expanding this at all, maybe make the levels a little more than just a big green square on the ground with platforms over it. You can see the edge of the world at all times and it makes it feel artificial. Maybe that's the aesthetic you're going for with big sky platforms, in which case it's fine. And lastly, the AI-looking main menu is a bad first impression. It makes it look like a cheap, fake mobile game. You can do better. The actual in-game art, simple though it is, looks much better. It's not even the quality of the art itself, it's just that it looks... thoughtless, if that makes sense.
Hope this helped!