Definitely seeing a lot of Binding of Isaac and a bit of Minecraft references. Intentional?
Let's do a step-by-step analysis, shall we?
Round 1: I like the momentum factor of the ball, gives you a bit more of a challenge. i think the only problem here is the heads, which spawn just one too many.
Round 2: Guiding "Isaac" into the slug is no easy task, and the heads provide just that much more of a challenge.
Round 3: Occasionally, the creeperbomb won't detonate when you need it to. On the whole, however, probably one of the easier rounds.
Regardless, the game looks really good, a couple of tweaks here and there and you'll be good to go!