I don't think FF has started to suck. I simply think teh novelty wore off thanks to all the spin-offs.
Used to be a new Final Fantasy title meant something huge. It was another installment in one of the most respected and beloved gaming series.
Then they started making sequels. Suddenly a new Final Fantasy wasn't a groundbreaking thing. It was just an excuse to make money.
Look at it this way.
YAY! NEW FF! FINAL FANTASY IX!
YAY! NEW FF! FINAL FANTASY X!!
YAY! NEW FF! Um..Final Fantasy X-2? Okay...
YAY! NEW FF! ..Advent Children?
Erm...Dirge of Cerberus?
*yawn* Crisis Core...
*snoreing* Dissidia....
*lifts head up* Oh...Final Fantasy XIII? Oh...cool I guess.....
You know, I think that may have been why I wasn't too excited for XIII. SO many other titles had come out that when XIII had come along it was like "cool I'll have to check it out"
I was excited for previous FF games to be released because they didn't come along that often. Now with all the spin offs and sequels (and most being pretty medicore) it's just not as exciting as it used to be to see a new FF title released