Trancevania DLC's Vampire has the most indepth storyline. This was the first dungeon crawler that I've ever made. Yeah, it doesn't really have that much character depth but that's not really the point in dungeon crawlers. I think that I made a lot better in the sequel though, which is why it became a finalist in an international game making contest.
If you're looking for 20h gameplay with romance, twist and stuff instead of just a simple dungeon crawler, I have made Adventures of Dragon which is epic length RPG.