People go into FFX-2 and FFX and see they are like night and day. The themes, tone, and very nature of the two games are polar opposites. It can be rather surprising expecting something in the line of FFX and then getting FFX-2, because of their radical differences. That's why it gets so off putting. You have a world and story that's living in the shadow of death, telling you a somber and melodramatic story full of loss, tragedy and heavy emotional content.
And then you get the sequel that is as lighthearted as a shoujo comedy anime, full of girls having fun, adventuring, and living in a world that's so optimistic and changed, people can't believe its the same setting. The change is extreme.
And no, she really isn't. FFX-2 is one of the most successful sequels and games Square's put out there. It's the very reason the Compilation of FFVII exists, especially AC. It was a springboard to many projects due to how successful its model was.