At first touch, I thought the controls would be too sharp, but I really like the feel the game had. Jumping was generally satisfying, though I did find myself wanting more of a "give" when jumping off near the edges of platforms.
The double-jump was well implemented as well, though I didn't realize I had it for quite some time - was there an indication of the new ability when I bought it?
A surprising amount of level content and back-tracking required from a short game jam. I eventually made it to the far end of the spikes with the double jump (my dash didn't seem to work when I got back to the main room?) Maybe some of that time should have been used to create another enemy type, or add some animation to the ones that exist though.
I think the stand-out feature for me was the shield. I loved blocking damage to heal myself.
I very much like how you introduced the player to new abilities through buying items as they play. Well done!