Here's a few things you can expect from Red Dead Redemption. Most of them great, but some of them not so...
1) A large Western sandbox. It goes without saying that for a game set in the fictional west you'll be spending alot of time on horseback or stagecoach. The world is huge and pretty and things are very stereotypical in that Rockstar manner
2) A horse that will annoy you. Horseback riding isn't as smooth as in Ocarina of Time, which is a shame considering. It's still very good, but expect some times where your horse doesn't want to come to you, or walks away when you go to him, or even randomly wanders through a cutscene and falls into the river.
3) Nice Real World Events. This is something all the other Grand Theft Auto games should adopt. It's a nice diversion when a guy runs up to you and says "They're gonna hang my wife and I don't have any money to give them". It's also really moving the first time you fail to save her.
4) Bumpy GTA:IV physics. If you played GTA:IV then you know what I mean, if you didn't then expect wierd things like ragdolling when you run into someone to fast, or randomly having your horse jump 12 feet into the air, or a stagecoach coming into town and just falling over on what should be flat land. It's less pronounced I imagine because the horse is smaller than a car in liberty city, but it's just as funny/annoying in a fight.
5) Decent gunfights. The targeting mechanic is similar to GTA:IV, except that while here it will lock to if near a target and follow you can easily pull you're reticle off them and move. No ability to swap between targets like GTA though. This one actually makes gunfights more fun, because unlike GTA:IV you don't see the health of the enemy. You only know their dead when the dot disappears off the radar (which is usually 1-3 hits)
6) No prostitute pickups. Sorry ladies, Mr Marsden is a married man.
7) Stereotypes. From the Wild West to Mexico to the Great Plains, don't expect this to be a near accurate American Western experience. The interesting part is you don't see Native Americans until the third act, and I only remember one Black bounty, and no Asian people so far. And everyone looks dirty, no matter where you are.
8) Political views. We hear you Rockstar, you hate the Federal government. Now less talk about it and more action please. Don't expect too many mission givers that want to chew you out about your backstory.
9) Wild animals. They're everywhere, and try not to get caught by a mountain lion while skinning a cougar.
10) Gambling! There's no way around it, apparently if you lived before the 1900's you were just gambling. Blackjack, Poker, Liar's Dice, Five Finger Suicide, there's alot of places and people who'll take your money if they can.
Now while this list is fun and good, its important to remember that the game doesn't want you to suceed so it's tutorials on games you haven't played won't be either well written or timely enough. It's totally possible to duel someone, before the game ever teaches you about dueling efficiently. Overall though, it's still a sold buy, just based off this as a single player experience.