Since no one is actually giving their impressions of the game, let me be the first.
As far as I'm concerned, there's really only one way to describe this game: GTA in the Wild West. Everything from the maps, the movement of the character models, the mission setup, everything screams GTA. Hell, the horseshoe game even feels a bit like the bowling game. And that's a very good thing IMO. I very much enjoyed GTA4 and I think it translates wonderfully to the time period. The storyline scenarios are very similar to GTA as well and are quite well done. And they have the same quality of voice acting as well, which is another way of saying they're quite good. The world is quite robust and you are always running into quickie little "help" missions or ambushes and they even have the nice little touch of people around a campfire at night in the middle of the plains who invite you to sit and chat. A very robust and very fun world to be running around in.
I ended up putting about 8 1/2 hours into the game. Was at just under 30% overall completion and was just about to get to the point you'd expect to after playing the opening (as spoiler-free as I can make it). I did end up doing quite a number of side missions (hence my relatively high completion percentage while never leaving New Austin) and even some of the challenges (was on my 3rd level of Survivalist) along the way. I'd say a 30 or so hour game would get you the vast majority of the way and that's a pretty solid length for a game like this IMO. I mean, you COULD go 60+ hours but that's doing very tiny little thing the game has to offer which to me would be a little much. And that's not including the multiplayer which I just never had a chance to get into.
Overall, I'd very much recommend the title. Is it a 95%+? Well, not really, but it sure is a solid 90% and one of the best sandbox games I've played, right up there with GTA4. Just too bad it came out when it did, with Alan Wake and Mario Galaxy 2 the same week. Maybe in the lull in the summertime I'll pick it back up (I bought it and traded it in under the EB Gameplay Guarantee, like FF13, so I only had it for a week). But if you're on the fence on this one, rest assured, it's a very well done, extremely polished titles. Still has the weaknesses of GTA (the "driving" feels a little stiff, character models could be a bit more detailed, sometimes it's easy to screw up without knowing it, the combat still feels like it could be better) but those are relatively minor complaints in a relatively excellent package.
I was there on that fateful day, were you?