Mainline, as in non MMO (and yea, I play FF XIV and I love it, but it's not a mainline entry)
X, XII, XV
Thankfully, XIV had made up for a lot of it. But I do wish we'd get a single player entry on the caliber of 4-12.
I have high hopes with 16. Chasing high end visuals was Squenix's bane these past 2 generations.