I'd say it's a testament to the series that this discussion is even being had. Sales are lower than previous games in the series (to date, its likely to close the gap some) but the notion of calling a game a flop just because of its sales trend against the same franchise is a bit excessive. It seems to me the drop in sales is less about Final Fantasy as it is a decline in the RPG genre and greater competition. If you strictly look at the sales of the game and compare it to other (console) games released this generation you'll find the following:
1) It's the 7th highest selling game in Japan; behind 6 first party games released on a console with twice the user base. (It has the highest attach rate of any japanese game)
2) It's the highest selling game on its system and has sold about 2.5x as many copies as the next best selling game.
It hasn't lived up to some people's expectations, but it's a blockbuster title, not a flop.
Primarily an RPG player but have interest in any game that will make me think.







