I thought this was great! It was a nice quick little playthrough. I personally thought the controls were perfect. There wasn't too much sliding that made me complain about it. There's more slide in big time games like Mario and Sonic. The added double jump made it forgiving. I also thought the graphics were well done. Not AMAZING, but very good. You could maybe add more polish and different animations.
Some small things that you could probably fix:
1. After level 1, I was collecting more starts than you said were in the level (In Level 6 I FOUND: 37 but IN LEVEL: 30, etc.)
2. Also, that boss would NOT have been beatable if he didn't keep his damage after dying. I would either make the boss a little easier when he's near death, or make some way to shield yourself. It's nice that I was able to win with the checkpoint right there. Just made it feel like a cheap win ya know?
Either way, I had fun playing. Thanks for making it!