As for darker titles, the four I'd really recommend are:
I Have No Mouth and I Must Scream: The last 5 surviving members of humanity are held captive by an insane sentient super computer who keeps them alive for an eternity of psychological torture. The prisoners must face their own fears, escape captivity, defeat AM (the computer), and die.
Sanitarium: you wake up in a Sanitarium after a car crash with no memory. Explore the worlds of your own delusions to uncover your past.
Blade Runner: Its like an alternate telling of the movie, the characters and locations are the same but the events are different enough to be new to someone whose already seen the movie. Multiple endings, each support the theory that Decker is either human or replicant.
AMBER: Journeys Beyond: Myst clone about a paranormal investigator and a haunted house. Pretty creepy at times, explore the house, find the ghosts, and then travel through their memories to put them to rest.
I also really like the humor of the Sierra and TellTale games.
Also if you're not opposed to SNES emulation I'd also strongly suggest Clock Tower and Famicom Detective Club.