Crusader: No Remorse | Origin | FREE (RRP: £3.99)
Talk about a blast from the past. Crusader: No Remorse is a little like a hardcore Sci-Fi Diablo crossed with Syndicate, as you'll exterminate your way through maps full of deadly guards and hazards with extreme prejudice.
I'm not sure how well it's aged, but on the other hand, it's FREE. I'll take it. Thanks to jaystan @ HUKD!