The only major issue I have is that there is a bit of floatiness at the end of a jump. It's hard to describe, but on screens with lots of smaller platforms it can be hard to precisely time a jump and not fall off at the end, especially when doing multiple jumps in a row. Like I have to fight against the inertia of the jump or the character will slide of the platform.
For example there is this type of screen where you start at the bottom, there is a minigun demon to the left, and platform "stairs" that go up and to the left with enemies on then. Try to jump all the way to the top in one go without falling off or taking time to adjust your movement on a platform. That's what I'm talking about.
Other than that, it's not bad, can be pretty fun at times.