Similar to fallout 3, the main city area is where you would find some massive action, but you also run into a few enemies when wandering the country. All highways and buildings are in tact still, just sometimes filled with massive amounts of zombies. There are still human strongholds also.
I'd actually like to see The Walking Dead comic be made into a game though its very likely that it'll turn out like crap, like most movie/book licenses.
If done right though, would really feel like a survival game. Scarcity of ammo, food, fuel, gunshots attracting hordes of zombies from miles away, cities holding the most resources but also completely infested, etc.
I dare you to look at a kangaroo and not laugh. I dare you!