Cave Story is a game with that classic old metroidvania gameplay. Exploring a vast network of tunnels and rooms, finding new items or weapons that change how you play the game, even to a degree that it might unlock the possibility of opening completely new areas in places you've explored. Weapons can also be upgraded with gems that enemies might drop on death. There are 3 levels of upgrades that give weapons cool, fun and often more powerful characteristics. Although while taking damage hurts you it also drains the weapon you've drawn of it's upgrade levels.

http://steamcommunity.com/id/HazeSteam/inventory

I remember playing through this game a few years ago and it caught me with the feeling of playing the good old super nintendo games. The weapon upgrade system in this game is something really interesting, it adds a quick sort of progression in the game that also gives you a greater reason of avoiding being hit than just taking health damage. Something that wasen't as immediately obvious back then is that the game actually has different endings to it, which proves games like this can have more depth to them. The music is aswell a work of art.

This game has over 9 thousand recommandations, that's alot, I mean just ask Vegeta.