As a former Dreamcast owner, I have to say that whoever told you that didn't spend much time with the system. It's true that Soul Calibur helped boost the DC's initial sales. But there were other solid games such as Sega Rally 2 and Virtua Tennis. Yes, there were bad games on the DC, but go ahead and name me a system that doesn't have a bad game.
Now, I did actually buy Shenmue, but I never finished it, as I got bored halfway. Instead, I spent the last of my DC days playing Sega Bass Fishing (I even bought the fishing rod controller for it!).