Doukutsu Monogatari ~ Cave Story is the best freeware game and one of best games i played because it has the best story & very good music. But i never would like it if i wouldn't try it. It is hard to beat till end, but not impossible. And most important it got me going till end, you could say i got addicted to finish it.
You can save the game and continue but not everywhere what is good. The bosses are made very good and you can find secrets and items. What was to me very important that nothing in this game repeats, every room is different but you can go back, not just forward. It was made by a guy named Pixel who made the game by himself !, he wrote the music and everything, he needed 5 years to finish it, it is also in english. respect.
Some screenshots, nothing to spoil the fun