FFXIII is the next game I plan on buying. I gotta hand it to SquareEnix, I don't play many video games anymore but SE I guess has brainwashed me enough to buy this one. I even played through FFXII, which was awful. I mean, it may have taken me a year on and off, but I eventually beat it.
However, the stuff like the sphere grid and linearity sounds fine to me, because FFX is overall pretty much one of my favorite games of all time (at least my favorite Final Fantasy despite my inevitable fondness for VII). Plus the open-endedness of FFXII was one of the things I hated most about that game (besides the terrible MMO battle system, of course).
So I'm there, whether it's good or bad.