Not saying this game is bad. In fact, it's pretty cool. It's frustrating, at times... but it's not bad. It's just that for something that "defines" next-gen (as the ad campaign claims) the game is missing something. It's missing some grit, or some polish, or something that I can't put my finger on as a gamer. It feels... a little half-hearted, maybe, is the thing.
Now don't get me wrong. I've played a couple hours of it, and I'm having fun wasting time (and occasionally people) in virtual Chicago, driving a stolen Challenger clone with my foot to the floor. But therein is another issue. The car physics are cartoony at best, and they lack the solid feel of Grand Theft Auto, which is what people will inevitably draw a comparison with.
And on the subject of driving, getting away from the cops is absolutely a pain, more so than it needs to be (especially in early 'fixer' missions where you're given a sports car and told to ditch the cops before driving it back to a set location.)
This game will do fine until there is a Rockstar title with the same mechanics to play with. Until then, we'll always have Chicago.