Great game!!!! I only played until World 1-5 though, the part where there are too many spike pits, I got frustrated and quit. I'm not really a fan of platformers to begin with though. If I have to repeat part of a level over and over and over again, I'm out.
Here's some constructive feedback...
~ First, here's what I really liked about the game:
1. The style and graphics were very nice. Very visually pleasing graphics. The use mulitple layers of parallax scrolling was perfect. The screen shake effects were great too.
2. Sound effects and music were all very fitting and felt good in the game.
3. Your tutorial was presented in a nice easy to understand way that flowed along nicely.
~ And here's a few things I would change if I was you:
1. The controls felt natural and intuitive, except I found myself trying to press "W" to jump multiple times. Since "A" and "D" are used to walk, it really felt like "W" should make the player jump. I'd recommend having it so you can EITHER press Space or "W" to jump! Have them both! And you don't even need to change your tutorial, just leave it as is.
2. The dust effect when you jump is just too high resolution. As is, it looks out of place along side all the blocky retro style graphics you have. I think having a dust effect when you jump definitely does add to the game, but please just make it more blocky! You could almost even use your graphic for when a bullet hits the ground, just make it a little smaller maybe.
Overall, from what I saw, the game seemed pretty great! Keep up the good work!