Buy it
The game has been out long enough for you to know about the quality of the graphics, and the style of the game, so I won't discuss those aspects.
Many reviewers are saying that they preferred the Ballad of Gay Tony over The Lost and the Damned. For replay value, meaning having to do the missions over again, I would have to say that I would I would play The Lost again before playing Tony. This is because of one simple reason, - I hate and am not good at flying/helicopter missions. I know the developers think it is cool to let players fly helicopters but there are too many helicopter missions in Tony and I have no desire to replay those missions.
I did like Tony and some of the situations and scenes are memorable, and some of the characters are very memorable like Yosuf, as well as Brucie and his older brother.
The Lost had a storyline that I wanted to follow and see what happens between Johnny and club president Billy Grey, especially when Billy Grey goes to jail again. Tony is just another storyline around rags to riches, pleasing various mob types, etc, etc.
Both The Lost and Tony tried to add some new pastimes but I only played them a few times. After being forced to take my friend out to play darts, bowling etc in GTA IV, I did not have much interest in playing the bar games or golf with my friends.
A much needed improvement over the older GTA games is the ability to replay a mission over again at a checkpoint, which at the very least eliminates all the tedious driving you had to do just to get to the mission launch in previous versions of GTA.
This is a game that you should buy for sure. It intertwines GTA IV events and gives you a different perspective from the new characters eyes, such as Museum Piece.
One of my favourite activites in any GTA game is hunting for hidden packages. Although I was glad that they narrowed it down to only 50, they are way too difficult to find and I had to cheat to find them all. In GTA IV there were too many hidden packages (pigeons) and I did not even bother.
Still, I say my favourite GTA game is San Andreas due its varied locales, and wide variety of activities such as shopping, working out, arena racing, dating, etc.