I reached the second stage once so far.
Wow. The game is amazing.
It looks and sounds great, controls and feedback are great too and the feel of the different weapons is well rendered. The enemy and boss patterns are good. The difficulty seems perfectly right on point from what I've played.
Since we're at this level of goodness it frustrates me to die while trying and not managing to mashing my bombs, yet how it works is probably pretty standard, I'm not certain, and I guess the theme integration is a bit lazy compared with how everything else is brillant. These are very little details.
It could be an arcade game just as is, nothing to change. Congratulations !