La-Mulana is an exceedingly difficult freeware game made in the style of the MSX (an old Japan-only computer, think Commodore 64). It's a freeroaming adventure platformer like Metroid or Castlevania, and is supposed to be sort of a fan-sequel to Maze of Galious. It took about three people five years to make and will take you at least 25 hours to complete, over 40 if you want 100% completion and access to the secret Hell area. Although there's not a whole lot of text, if you want to be able to read anything (unless you know Japanese) you'll have to download the translation patch and extract it.
I strongly recommend reading the HTML manual (included in the game download) cover to cover before you play. There are no tutorials or anything like that, and the fact that you can't save until you get a certain item doesn't help. Be warned, this game is HARD.
Recently it has been fan-ported to a few handhelds, too.