Alright, so after spending about 30 minutes with the demo here's what's in it.
Single player has Story, Challenge, Training, Player Data, and Replays. In the demo, the story mode only has Jotaro, Avdol, Hol Horse, and Dio playable. Probably the biggest letdown about this version is that it doesn't have Super Story Mode from the PS1 port, which had fights and a couple of mini games thrown in to break up the pace. You only get four fights in the demo.
I wasn't able to try out Multiplayer but I'm assuming it has local play in addition to online(it would be dumb if it didn't)
Another thing people were worried about is if the blood was censored out and Dio's Facegrab super. I can tell you that the blood is still in, there's a setting called Visual Expression which lets you toggle it on and off.
I'll have the full game tomorrow and I'll start taking my skills online with Jotaro and Mariah.