I really wonder how many of those people who "universally hated" XIII-2 actually played it. I really disliked XIII but I absolutely adored XIII-2. Fixed pretty much all the problems I had with XIII.
As for X, my least favourite Final Fantasy. Cliched story with twists I saw coming from half a mile away; linear as hell (seriously, this was the Final Fantasy which started "corridor syndrome"); most of the cast is absolutely terrible (Lulu and Auron save it from total disaster). Soundtrack is good and battle system is decent, though.
I have been convinced by a number of people (Brendude & Padib most prominently) to give it another chance, though, so I'll be buying the HD Collection when it releases so see if it's as bad as I remember it.
Not really. Final Fantasy has always been in a corridor for the most part. Try taking a " different path" in 4.