Hi castlebbs,
I'm just replaying the game again after a few months. Some suggestions I'd make are
-make the controls more responsive. It feels like it takes too long for the Zinky to get up to speed or to turn around
-make gravity stronger. It's a bit too weak at the moment and makes Zinky feel floaty.
-add some enemies. Lots of platformer games have enemies that walk back and forth or shoot at your character. Adding those could give you more challenges
Other than that, just create more levels. I think character control issues are probably the biggest problem right now.