Cave story is by far my favorite 2D platformer-type game that really clenches you with its story and gameplay.
(From the cave story tribute site):
Cave Story is really one of those games that can be considered a masterpiece of game design. There are so many wonderful and classic gaming elements, that I cannot even begin to describe just one quality well enough to say "It is for this one reason alone that Cave Story is a great game." There is just so much effort, originality and ingenuity behind this game and it really shows more and more as you play through it.It was made by one person, Daisuke "Pixel" Amaya, and he made it in his freetime over the course of 5 years.
Cave Story has many different versions now, such as Cave Story+ (on steam) and Cave Story for the wiiware
I'll add more to this post if you want me to, but please discuss this amazing game :o
(Right now I'm at Hell)
Gameplay of myself in Hell (Might be spoilers)