This one or two session adventure (depending how thorough -- and bloodthisrty -- your players are!) is a steal for under a dollar. Send your players into the darkness, where they will have to make some tough decisions as various forces of evil try to put the party against the others. Can they afford to take a stand for good, or will they be forced to compromise with evil to get the treasure in time?
I love giving my players moral quandries, and for a shortish dungeon, this has it in spades. I could see expanding this into an entire arc, with each section of the addventure becoming an entire dungeon in its own right. Definitely buy this if you want to watch your players squirm, trying to decide which villain is least deserving of their swords.