Having played the demo, I can say I'm definitely impressed with what you've put forward so far, but I can point to some areas I think could be improved.
Personally, the control scheme on keyboard is a bit clunky, while it can be managed with 1 hand, its very much awkward and caused my hand to cramp a bit towards the end of my first play session, the game also doesn't communicate that the player has a double jump very clearly. I also was unable to locate a method to quit the game from the pause menu.
I agree with other reviews stating upgrade boxes could be a bit easier to destroy, especially with a strict time limit.
Speaking of, I feel like the game is fighting with itself about being a timed moderately precise collect-a-thon, while also using procedural generation for the levels. It makes it hard to figure out paths within the time limit, and also makes it hard to earn any time bonuses to actually afford the upgrades.
(Of note, the grenade upgrade does not increase your grenade capacity, or start you with more in new stages)
I would suggest ditching or greatly extending the time limit, providing other rewards for completing with an excess of time- Or if you want to keep a very precise and snappy run and gun feel, I would actually say hand-designing levels would lead to a better game over all.
My other gripe, at current at least, is its a bit harsh to have to restart level 1-5 just to try the boss again.
Lastly I'll mention a minor bug that doesn't fit anywhere else: If you jump and hit a corner right while ascending, you can get launched vertically significantly higher than normal.
As I said, this is a really good game so far, and I had a great time with it, but there are some rough edges that could use some polish, and I genuinely hope you experiment with hand-designing the levels and upgrade placements.