"Your spaceship has crash-landed on an unexplored planet. You awake from unconsciousness to find your vessel ransacked by beings who have since left the area. Missing is a critical element of the ship's power core, without which you cannot achieve lift-off.
Donning your power armor, you follow a large group of unidentifiable footprints to a cave entrance set into the base of a nearby mountainside.
With limited supplies you cannot survive on this planet for long. You must reclaim your power core at any cost. Into the cave you go!"
Jeff Mather originally released his game Dunjax back in 1991. It plays out like a metroidvania style affair. Where you run and jump around the caves, firing and swiping with your halberd at anything that moves. The further you explore, the more you unlock.
Fast forward to 2015 and Jeff has released a Phaser powered version for the web playable on desktop and tablet.