As someone who spent hours on this game (I love it), better controls would improve the experience not to 5 stars but to 10 stars. Fixing random softlocks would also be amazing. I got stuck at the 3rd boss scene (after he flew into the ceiling and  never came out of it) countless of times. Once, after I took my power up, the 'blood portal' never spawned and I had to restart (I don't know how I triggered it). It's the little things that ruin the experience, but it's an amazing experience nonetheless.