Well the golden age of Square really ended with FFX. The only really decent game DEVELOPED by Square was FF XII and that in my opinion wasn't as good as the other in the series.
EDIT: I forgot to answer TC's question. Well, its really Square's infrastructure going down hill. They as a development team do not have it together. The most important thing when developing anything is: proper planning and teamwork and two thinking about the consumer. Square under their current leadership in their largest franchises have pretty much dismissed both points, but mostly point two I made. Point one can apply the most to FF XIV and Versus XIII. Point two applies to XIII currently.