Would be great, but lacks debugging and polish
The game is fun, the bosses are creative (the fro one was a great laugh in particular), and all in all, it's a great way to kill half an hour. I'd give this a 10 if it weren't for the major bugs and lack of polish.
Bugs I found:
1. Sometimes you walk backwards for no good reason. This is especially likely to occur on the first boss when he has the gun.
2. If you continue or restart, the missile boss in the first level glitches. He does a flame poof like he's about to fire, but he doesn't, and though his health bar will empty, he's invincible. Since you can neither kill him or die, the only way to continue is to completely reload the game.
3. The game says there's a reward for beating it without continues. I did so (even finished with 8 lives left), and there was a gold star on the title screen labeled PERFECT, but nothing was added to the menu. I tried playing again in case it had extra weapons, a bonus boss, or something like that, but nothing appeared to change. Of course, it's possible that the bonus is further into the game, and I'm just not seeing it because bug #2 makes it impossible to beat level 1 on a second playthrough.
As for the lack of polish, there's a couple of little things, such as the boss with the extended arm that tries to squish you being able to kill you a good few frames before he actually touches you.
It's a good game all in all, but I hope you release a V1.1 to clean it up, as it will then be a great game.