I agree that it helped fuel the Sandbox genre, and the open-ended feel was what made it popular. But that's not the same as being 3D. The majority of games are 3D, but not all of them share the same gameplay mechanics as GTA.
That said, the success of Chinatown Wars really depends on criteria. I think it's a success in some areas and a failure in others. I expected more sales wise, but it definitely exceeded my expectations in gameplay and reviews.







