As someone who doesn't play platformers nor retro games much, this game kept me playing over and over upon my first try. Firstly collecting everything, and later trying to plow through as fast as possible... I finally understand the appeal of speed-running - since it came naturally - and the greatness of simplicity.
Really fine controls and feel, and just generally enjoyable gameplay - yesss! Also, the sounds are great and I enjoy the lack of music, totally fits. I find myself making little beats on the ladders. The instant respawn with no waiting screen made it easy to keep trying, while the act of dying later on pushes you to rush the early levels to make it back. This definitely seems to help you attain a "mastery" of the controls and levels, and whew, it feels good!
I love it!