The gameplay is quite good and with an interesting twist. There's more than one way in which you're your own enemy, and what's even better is that the enemies can be your allies so they're also their own enemies.
I couldn't get past this wall here, though, because there was an invisible ceiling above:
woops, sorry about that. I've added a 1.1 version with the issue fixed if you want to give it another go.
Nice, I wouldn't have found out there was a boss fight if it hadn't been for that. It broke the monotony of the other enemies and while I don't know about whether bug fixes during the rating period are allowed, it would be a big shame if such a tiny bug made a large chunk of the game inaccessible. I did find out that if you "die" during the boss fight, you turn into an immobile pile of something and when you get hit, you get revived, though. That's probably not intended.
Some suggestions I thought of along the way: It would be fitting to add the trick where when the player stops holding down the jump button, their vertical velocity gets divided (for example, by 2), so that they have control over how high they jump - this would be very helpful in a bullet hell, where movement is probably the most important part of the game. It might be a bit more difficult to implement considering how there's also a double jump, though (it depends on how your double jump works). And another thing - since firing bullets at a rapid pace is what the player wants to do most of the time, it would be more comfortable to just hold down the fire button instead of pressing it repeatedly. It will also make the player feel more powerful if they can spray faster-than-normal bullets at the enemies. Not sure how many projectiles the game would be able to handle, though...
Lastly, I felt like the second level was more difficult than the third one, even with the boss fight taken into account. Then again, I'm not one to judge about level difficulty because my own levels are always terribly balanced.
