There are several things that need to be said.
1. The game did not bomb. I just didn't live up to your wild sales expectations. "10 million seller" "the next FFVII" etc...
http://www.vgchartz.com/forum/thread.php?id=63948
http://www.vgchartz.com/forum/post.php?post=3231193&page=6&postnum=1
2. If Final Fantasy wants to have a better reception then it needs to innovate in several areas. One of the main things it needs is a credible storyline. Basically the story of nearly ever Final Fantasy game is "spiky-haired emo youth with big sword saves the world". Look at Mass Effect, it was epic sci-fi space opera which something new and fresh (at least in video games).
http://www.metacritic.com/games/platforms/ps3/finalfantasy13
http://www.metacritic.com/games/platforms/xbox360/finalfantasy13