Interesting concept I say, makes me wonder how it'd feel if the mechanics were pushed further.
I think we all know how much the game can slow down due to all the spawns (which seem to include the off-screen ones).
Speaking of off-screen, I'm think that this game could greatly benefit from a radar that shows enemies, turrets and gems (and maybe even projectiles). This plus adjustments to the turret system (making it so that being in the turrets' line of fire easier to avoid + other varieties of turrets maybe? ) would widen the player's "area of control", give depth to the gameplay.