Gun was one of the best video games I've played this year. The gameplay and overall quality is very similar to the Rockstar Grand Theft Auto series. Of course, this game has an entirely different premise from GTA. It takes place in the Old West, and you get to play a sort of vigilante cowboy. You ride horses, do pony express and law enforcement missions, hunt wild animals, act as a rancher, and gamble. The story line kept me engaged through the end, and the gameplay was so much fun that I might end up replaying the whole game sometime soon. It's one of the better games I've played.
Note: At the beginning of this game one of your goals is to kill as many American Indians as possible. I found this very disturbing, personally, and was greatly relieved to find that the character ends up joining the Indians in their fight against the evil white guys.