I thoroughly enjoyed Driver 1 and 2 on the Playstation. They had open environments, challenging and cinematic cop chases, all set in an immersive environment which brought back fond memories of early films like "Bullit" with fun, Hollywood-esk chase scenes.
Driver 4 (Parallel Lines) and Driver 3 were not enjoyable for me. They added they ability to use firearms, ride motorcycles and wonder around on foot. Unfortunately it feels alot like the developers aimed for a GTA-like game and didn't have the resources to pull it off. The graphics look strangely warped, the vehicle physics feel wrong and the story line has very little pull.
I think, had they focused their efforts (and I'm assuming limited resources) purely on further refining their original formula of cars, cops and robbers, they could have produced something really great. But they did not.