Some Girls Are has that cliffhanger title that lets a reader complete the thought. And if what you said was suggestive of something less kind than sugar and spice and everything nice, then this book has given you the appropriate tone.
Regina Afton is a Regina George of Mean Girls dethroned by her fellow alpha bitch "friends" after a misunderstanding and forced to become the new school pariah. And the best quality of Summers's book is that she doesn't cover or shy away from the fact that Regina is, in fact, a pretty awful person. Most bullying YA has us instantly empathize with our protagonist because we see their torment is undeserved and often are victims because they lack a certain ruthlessness to keep that kind of cruelty at bay. We side with them because they are wronged but also because we like them.
Summers tells us that Regina does deserve hatred for what she did to others. At the same time there are critical differences, that some things nobody deserves, and the novel presents it with a cruel and lean prose that doesn't offer any moralizing. The first 4/5ths of the novel are brisk, tense and constantly making the reader horrified with what happens to Regina but also what she does to strike back at her tormenters.
I could not bear to put it down and didn't imagine how things would escalate. Whatever weaknesses usually found in bullying fiction, such as the almost criminally widespread ignorance of any authority figures, were outweighed by the authenticity of the feelings involved by the characters.
The last fifty or so pages take a major stumble in quality though, opting to drop the more difficult plot of Regina continuing her toxic payback for a romance. One that I really feel is unearned, which is a shame because Summers did a great job making Michael's struggles to forgive Regina for her bullying a truly built up to the moment in being friends, but it immediately goes from "I don't hate you" to kissing and then abandons all the more complicated relationships. That leaves the plot threads of Regina and Kara's mutual hatred and lack of forgiveness, or Liz's hatred for what Regina did to her conflicting with her attempts to be a better person, left unresolved.
And the resolution where the girls promise to stop bullying Regina because someone is finally willing to go to the principal with proof of it seems outrageous considering this has been widespread for years and is so endemic there's no way they wouldn't have been tattled on before. Especially with the principal turning a blind eye to the whole spray painting whore on a locker incident right in the beginning of the book. The happy ending is unearned, and it is more disappointed considering how well the story navigated its dark path in the beginning.
In summation, Some Girls Are complicated, and some girls are not. Sometimes those complications can't be adequately addressed in a novel under 250 pages. This is a worthwhile story for those who want to read a story that does deal with a very real problem in our society. It is compelling and doesn't flinch at the darker subjects. However, be warned of the ending becoming a little too neat for such a messy concept.