Eh, the design of Shenmue was pretty unique for both games. Instances where you can fuck up but continue on with the story, multiple ways of completing investigation puzzles, tons of ways to earn currency and spend it. There's a lot of little things that were done for that series that weren't done for any other action/adventure game.
Shenmue 1&2 are unique as fuck, but they aren't fun games to play. The best example of playing a game once and putting it down forever.