Knytt Stories, the sequel to Knytt (includes a level editor!) should be releasing sometime this month, next at the latest. I wouldn't call Eternal Daughter the "spiritual sequel" to Cave Story, though... it's not anywhere near good enough or similar in feel to be called that. It's just another exploration platformer, albeit a pretty decent one.

Have you tried Lyle in Cube Sector, A Game with a Kitty 2: Darkside Adventures (silly name, excellent game), Poyo, Spud's Quest or Noitu Love and the Army of Grinning Darns? All are great games that shoud provide quite a bit of entertainment value.