Great game but just too short
The gameplay in Gun is a lot like any other GTA wanna-be. Running around, shooting people only this one doesn't take place in the city put the old west. Basically your father gets killed (long story), and you have to find out who did while busting some Indian heads along the way.
The graphics aren't new gen neither are they old gen. They're basically keeping it up with the graphics to the modern age. The rocks and scenery could have had a little bit of more work but by the time you get used to it, it won't bother you. Sound is equivalent to the graphics. Although the hooting and hollering of the Indians does get kind of annoying you'll get over it. The value is not so great though. I thought $40 was a bit overpriced when it first came out. The price range of $30-$35 would have been better. Overall Gun has a campaign that is just too short, a great story, and some good side missions.
Rent or Buy
I suggest rent, and then, if you are a really slow player and you haven't finished the game by the time you have to return it, rent it again. It's just not worth it.