I can't talk for the internet reviews but many of the magazine ones for FFX were less than stellar for a Final Fantasy game. I'm not saying X got terrible reviews but for an FF title which is traditionally known for 9 or 10 or 4 1/2 to 5 star reviews I saw it get some 8 and other low scores (Edge Magazine gave it a controversial 6/10). I would also say (though this is my personal opinion) that X laid the groundwork for a terrible trend in RPGs.
XI's problem falls more into the fan backlash about making an FF MMO out of a numbered part of the series. Even then it has some terrible interface issues. Not to mention Sony making some bad decisions of dropping online play. Of course I personally feel the only real problem with XI (it is a good game though I despise PlayOnline) is that for many fans of the series don't count it and thus to much of the fanbase, there is a massive dry spell for a FF title which was filled with ports and sequels until the next true installment.
I like XII but as you said its gotten an odd backlash. Critics adore it but the fanbase seems to either be indifferent or outright hate it (and in my personal opinion for the most stupid and asinine reasons). Part of this is traditional hazing, the other part is that it changed everything so much. It also recieved heavy pressure due to XI not working out like it was originally planned and thus the game was trying to be rushed and placed under heavy scrutiny for taking so damn long to complete. I do feel a few years down the road the fan base will be more appreciative of this game. Especially since quotes I hear from the XIII team tells me its going to be more like X than I care for...
I just find that all three games were marketed and released poorly. X came out too close after IX so it can act as system seller for the PS2, XI has the fan debate about being an MMO which makes many people not count it, and XII took so damn long to come out that SE took drastic measures... These were all bad buisness decisions, and due to an odd marketing ploy of only building PR for FF,KH, and DQ they dropped the ball on revitalizing a few franchises (Except for Mana). It just seems to me that SE is falling dangerously close to relying too heavily on brandname recognition. I see hope with Last Remnant and and the new wave of DS original titles but I still feel that SE doesn't have any real direction for its franchises.
But to tie this back into the topic at hand. There seems to be some massive confusion about Versus and Agito. I feel most of the fans will only regard these two as side games rather than stand-alone. Part of it is probably due to the two games being made with systems very different from what the main series is known for. Versus will be an action game, and Agito is rumored to use a card game system. SE is known to put massive quality into the main games but confusion remains on the other two projects. Personally, I do feel Versus will be of high quality and chances are, it will be my favorite. Interviews with the XIII director has made my feelings for the game even more doubtful. Whereas interview with Nomura on Versus makes me realize he's got the right idea of what an FF should be.
(I never thought a day would come when I would say something truly positive about Tetsuya Nomura)