La-Mulana is an excellent 2D side-scrolling platformer/RPG that is reminiscent of 8-bit classics like Zelda, but with a much stronger focus on inventory items in adventure-genre style.
The game casts you as Indiana Jones-type adventurer who explores vast complexes, looking for ancient treasure. There is plenty of action, but also puzzle-solving elements that help "unlock" cool new weapons, items, and advance the plot. The game's attraction is easy to describe: if you like Cave Story or Akuji the Demon, you will definitely like this more "retro," but no less fun freeware gem from Japan. Note that although the game is entirely in Japanese, it is entirely possible to finish without understanding the language (although, like playing most Japanese-only console RPGs, you wouldn't understand the plot, and you may be bored at the need to mechanically talk to all the characters or revisit old areas repeatedly until something new happens). Be warned that it is *much* longer than Cave Story, though, so don't expect to be able to finish it in less than 20-30 hours. Two thumbs up, way up!