Like everyone else is saying, its a lot of fun. Could definitely see myself sinking some serious hours into a game like this. The art style is charming and unique, and the weapons and abilities are are quite creative. The controls and gameplay flow nicely as well. Don't know if its a bug but one play through my character just started taking random damage (with no enemies around) until I just died.
The portal was not very obvious to me, I though it was lava and should be avoided. It wasnt till I quit and did another playthough and then stepped in it by accident that i realized it was a portal to the next area.
Also, are you planning on adding more detail to the levels? I think that you could definitely add more cartoon details to the levels, they are very boxy and generic feeling at the moment. Maybe sections of the level can have different textures/colors/details to break things up a bit.
Anyways, great work. Will try and play more this weekend and see if I have some more feedback.