FFXIII doesn't really open up in the traditional sense, I think. Personally, it's actually one of my favorites, although I can see why many people have issues with it. I'm fine with the linearity because I think the pacing is excellent, and it has probably my favorite battle system of any game. FFX is by far my favorite and while I'll always love the simplicity of its battle system, I really found that XIII's had a lot of depth and strategy involved.

It's very linear, though, and it did bug me a couple times. I was aiming to get the platinum trophy but stopped because the only two trophies left seemed like huge chores to me (Treasure Hunter and L'cie Paragon, I have everything else). Still, I think it's a great game. Probably not for you, though.