Frustrating repetitiveness and lackluster characters indicate the decline of the once great GTA series.
The characters aren't really that likable. The main character, Vic, is constantly griping about how he doesn't want to be a criminal, they shouldn't be doing what they're doing, etc... Then he goes out and kills, sells drugs, steals military helicopters, etc... His girl is a white trash single mom who snorts coke with his brother behind his back. And his brother is just an all around A-hole. Of course GTA wouldn't be GTA if you weren't playing a criminal, but usually there's more of a likable charm about the main character.
Overall though, all of the GTA games, even poor ones, are lots of fun. The radio stations, guest appearances by Phil Collins, and general raunchiness, among other things, help to make this game worth playing.