The button for firing grenades being "r" makes it hard to steer and fire at the same time. The explosions being delayed and the enemies being invsible for half the time makes hitting them difficult. I found the optimal way to play was just upgrade speed and turning, then lure enemies into the room where you are targeted by explosions.
I'd suggest adding a "torpedo" that directly fires without costing anything. Right now, it seems like the player is incentivized to never fire anything and just kite enemies into dying in another room.
Fun game!