VeTrack: Well, I don't know if it can be considered underrated or whether the community at large already has it but I rarely see it mentioned here except during the release of Chapters and that sale. Maybe it's simply due to the fact that it's an adventure game and quite an old one... I'm talking about The Longest Journey. Its story is grounded in reality and not over the top, making it feel more realistic and personal. World-building is good too, it has books that you can read yet none of them is required to progress or to solve any puzzles. It practically has all the right elements that you would expect in an adventure game, even some time traveling (sort of). Lastly, the content is hefty and more importantly, very self-contained.

Fran67: I have to second your ideas. Haven't played those gamea but find your reasons very cogent.