Very ensnaring. I could get addicted to this, but there are improvements that can definitely be made.
My biggest complaint is the sporadic hit detection. Sometimes, the goombas don't die even when I shoot them point blank, and other times, when there are groups of goombas, the ones off to the side of the ones I'm aiming for die instead of them. Things like that.
Also, might I suggest in later versions, you incorporate different versions of goombas (i.e. armored goombas, different colored goombas that have different effects like green goombas inflicting poison or red goombas exploding upon death, even a giant boss goomba or something). That's not to say goombas should be the only enemy type. I'd love to see koopa troopas, bob-ombs, bullet bill traps, flying enemies like lakitus, etc, along with different versions of some of those enemies as well. That would definitely add to the intensity factor of the game.
I would also change the health powerup from the green 1UP mushroom to the red power mushroom only because it makes more sense.
The different levels can be better accentuated with different color pallets. Like Level 1 is fine the way it is, but level 2 could be the underground scheme instead to pay tribute to the original game you know? So on and so forth. Just throwing it out there.
I do like the Pac-Man take on having to collect all the coins to complete each level. That is quite interesting. And the movement is very smooth and fluid, a plus as well.
This has great potential for sure. I can't wait to see what improvements you make. Good luck.