Ellen Paige is ok, surprisingly NOT the same as her Juno character, which is nice, but also mostly uninteresting. Same could be said, really, of any other character. It's not that they lack depth so much as context - you don't really understand what's motivating them or what they're invested in, but you also don't really care that much. The plot bumbles from cliche to cliche, partly because all the non-cliche parts are so underdeveloped that you sort of ignore them.
The roller derby footage is ok, though much less violent - and carnivalesque - than actual roller derby - ie, less interesting and badass, really. It's the chick flick version of roller derby.
The most commendable thing about the movie is the ending, which is actually not nearly as annoying as you might think. There's a curious open-endedness to it (I don't want to give too much away here) that I found really interesting, especially given the obvious penchant for treacly sentimentalism in the rest of the movie - it's as though Barrymore decided to avoid the superduper happy ending, but compensated herself by cramming as much feel good chickflick goodness into everything that preceded it as possible.
Seriously though - it's not a good movie. It's not even a fun movie. It's really just kind of a waste of time.