Nice work! I think there are a few issues that a hindering it (in priority order):
- Not being able to shot UP while moving/jumping. This is my biggest gripe by far.
- Lack of diagonal shooting. Just copy Contra!
- Lack of verticality. Almost everything interesting happens on a flat plane. I would say go back an look at 1-1 in Contra for a great example of how to mix it up. (2nd level was better for this)
- Boss did not have clear feedback of when I was doing damage. I felt really confused about whether or not I was even hitting it.
- Way too much going on screen at once. Lacks pacing, especially during boss fight. I think a big part of this is how a lot of enemies and projectiles do not move in fixed 8 directions. It all feels a lot less predictable. I would simplify enemy movement and bullets to just move straight, in 8 directions.
- Some slowdown during level, and massive slowdown during boss fight.
- Exploding barrels that don't do damage!?! :D