Nice feeling of "alternate dimensions". I liked how the void's layout first seemed to be the same as the above world's one. The platforming was responsive, didn't have any hiccups. Interesting respawn mechanic, too. The knight in the title screen was well drawn, but I'm not sure why he's sitting like a ninja.
The graphics are decent, but there's some inconsistency - characters, trees and clouds are "low-pixel" art, while most of the floor sprites were "high-pixel".
Also, would have been nice to see something more "epic" at the end than just collecting a few shards.
Congrats on your first "published" game!