This is an extremely impressive entry. Feels a lot like an old 8-bit game. Like a lot of others, though, I lost steam in the second area when I needed to collect powerups before moving on. Tweaking some things to make it a little more fair would make this game magnificent. For example, the weapon range could be extended, or the gravity could be tweaked so the player can more easily jump over enemies, or the player could have more health regeneration options, or enemy placement could be tweaked to create fewer near-impossible situations. Really impressed by this though, especially considering this is a solo project. Well done.
Oh, and I'm sure you're already thinking about this, but some sfx on the player weapon firing will help improve the feel a lot.