It was one of the first games that allowed you to go anywhere, where you could miss time specific events by being at the wrong place at the wrong time.
Also 3D was still new, and this was a big world to explore. If you had money in the game you could go to a gumball machine filled with trinkets and buy them. It tried to create a virtual world where you would do more than just run around, and beat up a group of people over and over like most games during this time of gaming.
Games since have done this, and like I said, now are much better. Shenmue was a crown jewel to a system that died a premature death. Dreamcast is still a system that is still talked about on the webs, so it makes sense that it's most revolutionary game is still talked about too. Personally, when I had a dreamcast Crazy Taxi, Sword of the Beserk, and PSO were my favorite to play. and any sports games when someone was around.
