The series didn't become big because it was 3D. Games became 3D during the 5th generation, while the GTA series became popular during the 6th generation. Rather, the series became so mainstream because Grand Theft Auto III was an incredible title, and one of the first big titles for the PS2 (this draws similarities to Gears of War, albeit with more appeal and sales).
There's no good excuse for the sales of Chinatown Wars. If you're satisfied with them, more power to you. Take 2 seems to be fine with them, and I'm sure they will make a profit. I'm disappointed due to the hype, the game's reviews, and the enormous popularity of the series, but that's just my opinion.







