Grand Theft Auto IV
First off, look at those graphics. Compared to the other GTA's, they are amazing. They look so real. Normally, I don't really care about graphics (the gameplay is much more important to me). But these are so good, that I can't help but be amazed by them. I've played past GTA's before, so I know the gameplay will be fun. I love open world games like this, and this city looks amazing. Another reason why I love GTA is the detail, and all the previews I've seen for this game have shown tons of little inside-jokes and small details that I'm really excited to play.
This game looks so good to me, that I am actually going to go buy and Xbox 360 just for this game. I've been wanting one for a while, but this game make me 100% sure that I should get one. This one game is affecting my purchasing decision. I've got the cash, I'm just waiting for my checks to clear and for the game to be in my hands. Then I'm heading out to the nearest store to get me a 360. Then the following months will probably involve just me playing GTAIV. I can't wait.