I can understand where most people are coming from. We're so advanced in technology nowadays where we should have games that should meet our expectations.
Remember when VII first came out and people were mind blown how amazing of a game it could be just on the PS1?
I can't really judge XII on the PS2 because I never played it, but I can tell it did try something new with their whole battle system and game play based on looks.
I think XIII series really innovated us with just a good battle system and graphics. The story itself can be judged on your personal gaming preferences, but I can see where they're going with XIII. The XIII series is supposed to be like a modern movie with stereotypical characters that you could relate to with their own interpretation of their Final Fantasy world. XIII also has psychological traits like humanist themes and establishing one's worth. People complained about the linearity. They gave us XIII-2 with fixed game play, however I feel as if they damaged a great story that established in the first game. XIII clearly does a better job at story than gameplay, and hopefully Lightning Returns can balance between the two.
TL;DR, were you really disappointed in the XIII main series itself?
" Serah, Lumina, and Vanille playing "Triple Triad" together. " - Romangelo
For XIII I was expecting at least a mildly entertaining game, is that too much to ask, SE?
I had absolutely no expectations for XIII-2 because of that and well, it was half-decent I geuss. Hype is pretty risky, I suppose; it can get you more sales but you might end up over-inflating the game.