When I first read that Diety was a stealth action game my first thought was of the Thief series. When I played the game I was happy to find that it wasn't just a rip off and the game was quite different.
I guess you're some kind of demon or something, didn't really pay attention to that part. Light hurts you so you have to stay away from light areas, you can travel via torches to stay invisible to your enemies, going to a torch "converts it" and changes the color to a dark purple. Converting torches is also what heals you.
I love the fact that the game forces you into stealth. If you make a frontal attack it will actually damage your health, where if you make a rear attack it will heal you. The game also has a chain system for travelling, making a chain you can go from a torch to attacking an enemy then back to a torch again, hopefully remaining unseen.
The game is very short, only 4 levels long, but it's free on Desura and it was four levels of great enjoyment for me.