I personally really liked it, but I sometimes wonder if it helped glorify the "villians" a little too much. Zombie spent the majority of the movie trying to get you to feel uncomfortable because of their actions (the rape scene was expecially disturbing), but then all of a sudden we're supposed to sympathize. I think what bothers me about it is not so much that it felt like it was too little too late, but it actually was effective enough to work fairly well, but I'm not well enough for me not to feel kind of bad for it.
On the other hand, that was probably his intentions. The movie really is one that will screw with your head well beyond anything shock value can deliver (which makes it far superior to the first one). In the end, the villains aren't so much disturbing as is your willingness to sympathize with them after they have done all of those horrible things. It really is the grand finale in that plan. He builds it up with the development in their relationships with each other and by showing the ugliness of the "good guys." When the Free Bird scene comes up you find the lines between good guys and bad guys so blurred that you begin to shift your sympathy with the Rejects because of the atmosphere that the song creates. So I guess, ultimately, it worked. I just don't like being messes with, I guess. Why do you do this to me, Rob?!