Tried it out. I found it fun enough for a few hours.
In my opinion i found it a little too easy, run ended mainly due to the upgrade that said if you dont move you deal more damage which i immediately bought.
A Couple Thoughts:
-predictive enemy aiming
-grenade type attacks
-i saw a player can use mines, enemies using them too might be nice addition
-maybe not your plan but making player drive with momentum instead of instantaneous movement would up the difficulty.
I do have a little background with bullet hell like ROTMG, which might skew my difficulty read.
Anyways looks like a good start, has vampire survivor feels.