I love GTA4. The game is simply amazing. If you have been in New York you see so many great places again. The shooting parts are finally fun and everything really fits beautifully together.
I had more fun with some games this gen but only 8-10 hours. GTA4 is one of the best games I have ever played. No other game created such an awesome world.
And for those who are saying that there is less to do than in San Andreas:
1) How much time do you have? You can do the storyline, races, hunt bad guys, steal cars, play darts, pool, cubed, go out with friends, fly helicopter, drive boats, make stunts ...... Most of the time I am overwhelmed by the possibilities.
2) This is the first game of this gen. They had to create the game engine, art work, characters, cars, and the game is still huge. Wait for the next 1-2 GTA games for this gen where they only have to rearrange the already made artwork like they did for San Andreas.
Bottomline: Awesome game. And for sales: 9 million copies sold and still >200k per week? Thats ridiculous.