The one game I have to recommend is Sanitarium. It reminds me of Torment in some ways. You wake up in an asylum, covered in bandages, surrounded by insane people. The plot keeps you on your toes, and you don't exactly know what is going on during the game. Clues only bring more questions. Everything around you is twisted in some way, and it gets wierder as it goes along. Great atmosphere, mature approach/themes. It's a must.
I also recommend Blade Runner. It captures well the great atmosphere and world of the movie. Investigations and case solving replace the usual puzzles. There's also some randomization in some events and clues that, along with some choices, make for a different ending.
Personally, I don't see what's so great about The Longest Journey. It's a solid game no doubt, but it seemed a bit too childish to me. The themes are quite mature, but many are presented in a simplistic way, IMO, almost from a child's perspective. It might float your boat though, it's very lighthearted.