i always have a soft spot for stencyl games because that's what i use for the most part when i do want to make games.
i liked the intro a lot, but it didn't feel like it tied in, like it was anticlimactic.
the visual aesthetic is interesting and it's good that you added the particles for the impact
the movement is very floaty and you can get stuck on walls, if you wanted to change the getting stuck on walls, change the character's friction to 0, or set the material to ice, which does the same thing, and also change the player's velocity to 0 when no keys are pressed.
one of my favorite things so far is how the platformer robot dies after getting pushed into the wall, splitting up into different things
if you want to have the player be able to push enemies around, it would make sense to allow players to jump off of them as well
one element in the level design that i particularly liked was when one of the horizontal platforms was moving under some tiles and you had to wait for it, i dunno why i liked it but it feels nice for some reason. i think because it goes into a hole at the side of the level it makes the level feel less constrictive somehow, even though if you removed the hole it would be the same space for the player to move around in.
the sound effects are a bit loud and long for comfort, and the sound that the player bullet firing makes is inconsistent with the rate of fire, if you watch this video you'll maybe get some more ideas for how to put sound stuff together, he says it better than me
also, it's nicer for the enemies to flash white or something when you hit them, more visual feedback is always good, jan willem nijman from vlambeer talks about that and other stuff in this video, some of it you already utilized, but it would be nicer if you covered more bases. https://www.youtube.com/watch?v=AJdEqssNZ-U
i also liked that you could break coins from a far distance
in parts where there are a lot of enemies the sound effects are honestly painful to listen to all clashing together so i had to turn the sound effects off after a part where there were a lot of enemies. i think there was something about that in the earlier sound video i linked
also, the resolution is a bit high to comfortably play in my browser because it's automatically enlarged for some reason :P I'm doing a thing with a similar size (640x640) but it's only because it was a direct sequel of sorts to my first game, which was at 640x640 and i wanted to keep it consistent to wrap it up.
overall, some elements are flawed but it's an interesting thing and both makes me interested to see what you'll do in the future, and motivates me to do my own somewhat large and awkward stencyl game that most people probably won't finish.
sorry if i seemed condescending or annoying, i've mostly only made really dumb strange games, i just wanted to try to help steer you in the right direction