Nice start! I'll definitely keep an eye on this. As you mentioned, it's still in an early stage of development so I'll have to see more before I can give a lot of feedback.
So far, I like the graphics! The enemy sprites look nice, I like the cat theme. I kind of want to see the slime be cat-themed too! Maybe ears and face?
The music is pretty good! I liked the track in the Abandoned Mine the best! I'll have to try out Labchirp. The sfx sound like a step up from the Bfxr stuff I end up making.
Nice work, looking forward to the next version!