F***** AWESOME! But i would actually give it a 9.8 out of 10 instead of Perfect.
Personally, I would give GTA 4 9.8 out of 10, but Gamespot changed there rating system last year. GTA has a lot of depth in the game like "decisions." GTA has moments in the story where you have a decision to make which will change the game itself like the ending.
Every inch of the map has full detail like the civilians, water and even buildings. You can see the buildings from different ends of the map, unlike San Andreas or previous GTA's where the buildings or objects pop up.
The game also added new features that keep you playing it. In GTA, you get a cellphone which allows you to make calls or access online multiplayer. The cellphone helps you call friends and girlfriends. Once you call a person that is your friend, you can select and activity to do with that person like drinking or darts. From here you build relationships with people. Once your relationship is high enough, you unlock special abilities from your friends.
GTA is almost perfect but there are some things I believe reduce the 10/10 rating.
For starters, after beating the story there isn't much to do. You have a few options, go for 100%, play online, or mess around. There isn't player customization like in San Andreas, you can't get a haircut, you can't customize a car or even change your appearance. There aren't many options for you to do.
Then there are a few glitches. If you drive really really fast for a bit, the detail of the map vanishes and then pops back up.
In the end, GTA 4 is a phenomenal game and everyone should at least try it.