But to be honest, it's not just dreamcast fans. It's sega fans, non sega fans, and people who are gamers in general. Including Virtua Fighter fans. Best way to find out for yourself, is to play Shenmue and see for yourself.
I will admit, the game series is overrated to some people, but it's one of those games, that live up to it's hype and legacy. It was revolutionary for its time, set standards for open world gaming, and did stuff that people and game devs thought, was impossible to do, or program into games.
Like Shenmue, another example of a revolutionary sega game, is the famous 3d fighting game called Virtua Fighter. And even to this day, Virtua Fighter has not been equalled or surpassed yet, especially when it comes, to Virtua Fighters gameplay and combat. The interesting thing is, both Shenmue and Virtua Fighter, are sort of related in alot of ways. And both are made, by the same creator, Yu Suzuki.