I just checked their website about that earlier tonight, supposedly you can *only* play online.. but they may add some offline play before it goes final.
The full online play is alright in my eyes though. You can set all kinds of options if you create a race (max horsepower allowed, max level, minimum level, set wagers etc) so you can create/join a race which is just right for your current skill level. Also, there's time trials where you can make money and not have to play with other players (which is real nice for the beginning of the game)
There's only one problem with the online play. They say it may cost $10USD/month to play
I own 1,3,4 and Porsche Unleashed, PS is 4 my comp, i'll admit to never playing N4S2, i know it has wickedly awesome cars in it but whenever i go to either rent it or buy it, it isnt there, what a drag.