I had a lot of fun with this one. I really like the concept and I'm going to come back to it and try to get all the items.
My only 2 complaints is being able to pick up items when a you already have one, and having the 2nd one just disappear. I'd rather just not be able to pick it up. The 2nd is it almost needs a really brief immunity period after getting hit. Doesn't even have to be more than half a second, but I died because I got stuck on an enemy and it just ate the last quarter of the health bar almost instantly.
I love this overall! I'd play a full released version of this easily. I already want to play more now! Great job!