Yeah, art and music is pretty weak. I have a couple artist friends that I can get help after the game gets more finished.
The gameplay music was even worse, I found a new one like just before posting the demo and I am not happy with it either. Main menu music is cool but it has some vocals and it is not looping.


>  - Constraining the cursor to 1/4 of the screen feels weird
I was thinking giving different range (for cursor) to different guns would be a good idea but it is more bothersome so I guess I will just scrap the whole idea and make cursor like a mouse.


> - Action being interrupted by the level up screen is not okay

You can delay leveling up by pressing esc. then it does not pop up anymore, you can open levelup menu by pressing tab again. I can put an option menu to make it neven pop up until you ask it to.

> I can play the game in one corner and just ignore 3/4 of all enemies. Intended?

Not really intended, enemies have certain radius which makes them follow the player. This range gets higher as the time goes on. And some enemies ignore this range (randomly).
Maybe I should monsters less random, even if they can't see the player, they still might try to randomly approach it, half the time. Forcing monsters to spawn outside of screen does not help either. They can spawn on edges though. I am aware of this problem will definetly try to improve it.

>  - Enemy slowdown is an upgraded reflex boost, since it doesn't slow down your reload and fire rate

Yeah, I should buff reflex boost a bit. I first implemented reflex boost because it was cool, then implemented slowdown which was because easy to do :)
Reflex boost last longer, I can buff it even more (make player faster maybe) or nerf enemy slowdown. I was thinking reflex boost would help you to aim better and move more correctly.

>  - Weapon drop needs to be spread out more. Got 3 weapons at level 2, the next one at level 7
Yeah, it is completely random. Spawn rate should be more like dota's randomization. It gets higher and higher until it procs, then it reduces to minimum value.
Another problem is probably weapons spawning outside screen. I should disable this too. Pick up range will be increased too. And I will make them easier to see

>  - Rocket launcher confirmed OP. That reload time is ridiculous
You are correct. Most weapons are very currently and rocket launcher is one of the strongest ones.