Doukutsu Monogatari
This is one of the best freeware games I’ve played. The sentiment is echoed all over the world, as well. Think of the game as Metroid, except you’re not a chick wearing armor but a guy wearing normal clothes. Confused yet?
You play the part of a nameless person who is off in a quest to help out a race of creatures named Mimigas, which are being kidnapped by an evil doctor who… well… you’ll see.
Unlike many other adventure games, Cave Story is heavily story driven. And the game is long. Very, very long. And full of secrets! You’ll have a great time trying to find everything. And trying to unlock the three endings.