I've played it. It's not as long as the original, but it does add a lot of extra features and things to do. The Don's View is a neat idea and is executed pretty well. I had a lot of fun with the game, but I didn't play multiplayer and I have heard that it is pretty disappointing. The DLC released in the last week I think was also kind of lacking.
There are a few reviews out there that give it a <5 including gamespot. It definitely does not deserve a rating so low.
Overall the game took me about 14/15 hours to beat the story. It could be done quicker, but I took my time and made sure that I completely killed off every member of the rival families. I guess it's up to you whether you spend the money on a game that you will probably only play once or twice.