I'm not normally one for themed, seasonal gaming... but Halloween seems to lend itself particularly well to playing a particular type of game.
So what are you playing this spooky season?
This year, I'm playing through Castlevania: Dawn of Sorrow (DS version, via the Retroid Pocket 2S). It's not the spookiest entry in the series, but has enough creepy castle exploration to fit the bill.
Super Metroid is an unintentional horror game.
The sense of horror and dread seems intentional. Dead scientists on the ground, dead soldiers on the ground, eerie music, limited items at the onset, etc.