The game is just beautiful, and the first half or two-thirds is really great as you settle into the Western milieu, learn/gain the different skills you'll need, and explore the world and the story. I'd say the last third starts to drop off in both quality & fun as the game has now run out of new tricks to teach you, and the focus turns more and more to killing passels of bad uns. I also think the Dead Eye (a slow motion effect that helps you dispatch your many foes) may actually be too much of an advantage. Don't get me wrong, I still get killed from time to time, but the Dead Eye makes it sadly easy to waste a bunch of dudes.
I guess Rockstar must still feel the burn (so to speak) from Hot Coffee, but it's still a little weird that the most you can do with the many, many lingerie-clad filles de joie is tip your hat to them. Well, you can knock them to the floor and shoot them in the gut, of course, that goes without saying.
I found the treasure-hunting side-missions strangely enjoyable. There's very little 'game', it's just about noticing the natural feature depicted on your treasure map, and then recognizing them when you come across them as you roam the landscape.
Lots of nice details everywhere. I saw a guy stop his horse and suspiciously (I thought) skulk off the side of the road. I followed him to see what he was up to, only to find him taking a leak on a rock.
The AI poker players have 'tells'. Even the guy who doesn't speak a damn word.
I haven't tested out the online multiplayer yet. Maybe soon.
As for minuses, besides the weakness in the story at the end, there are some issues with bugs (none too serious) and some issues with control (sometimes frustrating/bewildering, but mostly only with things you don't do frequently).
But really on the whole a great game.