Probably the main problem with Driver 4 is that the developers tried to make a GTA clone, but didn't know how to do it. Driver 4 has nothing to offer and is one of the simplest and emptiest open world games I have ever played.
The game lacks interesting content. The city is very empty and boring, with the only a bit entertaining form of side missions being circuit racing, which after a while gets very repetitive anyway. Other than that, there are some collectible stunts and that's about all you get in freeroam.
The story itself has an interesting premise, but is not very well executed, plus the main hero is bland and easily forgettable. The missions are not very interesting either. Most of them have simple objectives like "Drive a car from A to B", "Go to B and kill C", "Take the car and loose the cops".
Where the creators did succeed, though, was the great atmosphere of the 70s supported by a wonderful radio soundtrack.
The second biggest problem of the game are controls and car handling. Yes, a game that's called "Driver" has a bad car physics and handling. It takes most of the fun from driving, which is especially troubling in a game where you use cars 80% of the time. And thank god for that, because those other 20% are missions on foot that really show the developers' anti-talent for TPS shooters. The controls are clumsy and slow, which really doesn't help the terrible shooting mechanics and makes the action parts of the game downright irritating.