A graphical improvment over San Andreas but it feels like it's lacking in content.
While your character is still customisable, there doesn't seem to be as many ways to customise. There is no longer an RPG side to the game. i.e. you can no longer upgrade the characters skills and physical attributes. This also leads to a feeling that there are less activities throughout the playing area. There are no longer Gyms to attend or training centers for the various vehicle types and only 3 stores to buy clothes in. Neither can you change your characters hair style. I also felt there were less side missions available in this newest installment.
The story and characters as always (In the GTA series) are great with a good mix of the dramatic and funny. Some of the new characters are probably the most memorable of the series. The radio stations are excellent and provide many a laugh as well. You may notice my review feels like I'm just comparing and contrasting to previous games and you'd be right but this is only because there are simply no new features introduced in this installment. If there were something original here I could review it on its own merits but everything in GTA IV has been done before.
To summarize, it's worth playing but personally I don't think it warrants the 10/10 that game spot have given it and I dont think it's an improvement on San Andreas.