Graphics are meant to be retro, so I can't really ding for that, but there is a reciprocal expectation for gameplay. After trying nearly every button to switch between missiles and mines, I still couldn't find it. The controls in the comments do not remind how to do this and it is impossible to progress without it. This is a very minor issue in an otherwise fairly standard linear platformer.
The boss battles are well balanced and reminiscent of Mega Man. The exploration should feel a bit like Metroid (NES) but with a bit less freedom. As with games of this type, the new tool/weapon progresses you through and sometimes aids you in boss fights.
A little slow paced waiting for the invincible monsters to get out of the way, but not a bad game.