Nice take on the theme :)
I think that was a nice top down shooter. That was fun to play. Of course lacks of game juice, but it's normal for a prototype.
A few things I wanted to point out : the enemies doesn't deal you damage when you touch them and the menu buttons are very small so aren't at gameboy's resolution and can only be clicked with mouse (there is no mouse on the original GB). Also I think a pretty small thing that actually does a big difference is a background for the ground.
The game felt silent but, once again, it's okay for a prototype.
Good job you were able to ship something in time !