I hesitated for only a moment on whether or not to call this "a new game". Although the version I played comes on a standalone disk that I bought at Best Buy and doesn't require your Grand Theft Auto disk or saves to play, it contains two episodes of the game that were originally released as downloadable content over Xbox Live. According to the achievements, that means this game is actually a part of Grand Theft Auto IV, which was released almost two years ago. I'm using the traditional definition of "new game" on this one. I went to the store, I purchased a game disk, it's got two new adventures on it that I've never played before. To me, that counts as a new game.
I haven't made it very far yet, so I'll have to return to this post at a later time to give it a final review after I've beaten both episodes....but so far, it's just as entertaining as Grand Theft Auto IV was, and I'm really enjoying it.
Overall score so far: 9/10. Grand Theft Auto IV is one of my favorite games of all time, and this is just more of the same. Brand new adventures with new characters, it's good stuff so far.
Here is the achievement I've unlocked so far.