I always forget which one Red Dead was in that tidal wave of old west games that were on the 360. The summary for all of them though was more-or-less the same: interesting idea, fun mechanics but average to poor overall experience.
Now, a big part of that was that none were as open as they all promised to be, so if this game does actually play out like the videos makes it seem that alone would make it a worth-while experience.
As for the online stuff, there's been a lot promised like it, but that video is pretty convincing that they cover everything someone could ask for in free roam online play. Especially the bits that seem to show a player of the opposite alignment would get if not experience than some sort of reward for halting the progress of someone's missions. That is just tits.
I haven't said anything helpful though. So tldr; if it does those things it will be a good game. If it doesn't it wont. I'm confident that Rockstar is a company that could pull it off, though.