I would skip 13 if I were you, but everyone I know that loves the FF series was dissapointed by the major changes.
1) The game is literally a hallway. You walk in a straight line the entire game.
2) Combat is real time instead of turn based.
My friend said she liked it so I gave it a try but I gave up after an hour or two.
I can't tell you if the plot gets better, but from what I played the plot was all over the place. They go for a mystery kind of plot where you have no idea what's going on initially and 2 hours later I still didn't fully understand what was going on. Something about a prophecy, genocide, and the end of the world.