I don't like 2d sonic games and this was probably the best 2d platformer i've played period.
Answer is Cave Story.
Shovel Knight, Cave Story, and Freedom Planet are all great games. Good taste in this thread. But Cave Story takes all of them for best indie platformer no contest.
Even though freedom planet is a good game all of the stuff in the "what I expected" category is still there
See: the story, the voice acting, half of the characters