I played all the levels! I think level 2 is kind on hard because is kind of long and all the spikes, we just get to known the slow mo mecanic and there are a lot of rooms with spikes and hazards, then the next levels feels easy and short, maybe you just need to move it to a later level. The rest of the levels feel more balanced acording to the level number.
I also find the mecanic to return enemy proyectiles really cool! I would like to see more of it but I understand that you guys didn't had enough time to add a lot of levels.