I found no flaw in the controls.
Yeah, I don't see the issue either. I found the controls very intuitive. I also love the music and the general aesthetic of the game. It's kinda... retro? But not in the usual ATARI or NES way, more in a 1990's Apple 7 or Windows 95 kids' game way, which is really appealing and original.
My biggest problem would be the lack of levels. Twenty is not alot - forty would have been more like it. The fact that the game kicks you back to the menu after beating each one (if you've beaten the next one) is annoying, particularly when you're playing through a second time on Hard. There should definitely be a button to lower quality (it worked just fine on my PC except for the fade-out effects). There are also a few points on Hard where it seems basically impossible to finish the level due to poor enemy placement. I'm thinking of Level 13 in particular - those two turtles are just placed in the right way to make the timing completely ridiculous for that one jump.