Saw this lurking as a guest, couldn't help but check it out.
First off, try to code in item drops from enemies, like small energy and large. Also the knockback and invincibility as mentioned. Beat the level on the second try. Things to note:
peashooter bullets go through walls and the limit onscreen is three.
try to change controls to Z for jump and X for shoot.
the enemies fire randomly, try to set up a definite amount of things.
But the engine's pretty good.
Health should work like a sidebar thing in Megaman, with 28 units of health. I think small energy was two units and large energy is like.. I'm not sure, 10 or so? It was a lot more. Same for weapon and weapon energy pickups. I'll go record this maybe. I don't know.
Bug: If you release jump when jumping, you immediately go down. You should do that jump thin like in Mario.
That's how jumping worked in Megaman, so it's not a bug. It needs to stay like that. Research games that clones are based off of before you post "bugs" that could be in the basic movement engine.
And with that, I leave again. Or maybe I'll go post in /ee/ about IRC. I don't know. Yeah, I'll leave. Adios~