Check out Desert Stalker. It's post-apocalyptic or Mad Max setting with hints of sci fi, horror, and supernatural elements. I discovered it about a month ago, this was my first experience with adult games and after trying a number of others I think it's still the best. Good story, great visuals, adventure game elements with branching storylines and the best "harem" mechanic I've seen so far.
(But I am also interested in this thread, to see if there are other good games out there with the same vibe!)