Awesome, but not the best in the GTA series.
Music: I know Rockstar spends hours choosing the right songs for its games, but I still feel that San Andreas still has the best soundtrack in the entire series. I even liked the music in III, and Vice City better than IV. One of my favourite activities in any GTA game is to just drive around an listen to the radio. In IV there are too many radio stations, too many songs, and it is hard to find the songs you do like. So, when playing IV, one of my favourite GTA activities has disappeared.
Hidden Packages: Another favourite activity is finding hidden packages. In IV, it comes in the form of 200 "flying rats". 200 packages is overwhelming to the point that you think, "why bother". Even with a cheat guide, it could be next to impossible. GTA III did it best with the hidden packages, - you get rewarded for every 10 packages you find.
Graphics: I prefer realistic character modeling in games, I was put off by the cartoonish art style of the characters when I first saw the cut scenes in GTA IV. Roman, especially looks cartoonish in his scenes.
Side missions: I still like all the character customization in San Andreas - the clothes,working out,tattoos etc. Also there were more side missions in San Andreas.
For these reasons, I was slightly disappointed with GTA IV, and would not give it a 10, but would still give it a 9.