Better than I expected, I especially appreciated that at the core of the story there is an all-female friendship instead of the usual love drama. On the downside, the two main characters are utterly insufferable: one confuses badass with arrogant and "stalkerish", the second is a modern version of the Victorian "damsel-in-distress": sickly, fragile, always in need to be saved. 
 It seems that a YA worth of its name can't live without a character that wants to control the another and call this "love". In this particular case friendship is the reason of Rose's protective attitude towards Lissa but this doesn't justify her spying on Lissa, especially since this spying consists in slipping in her head. 
 Mead doesn't write badly, particularly if compared to most of paranormal fantasy authors but she isn't neither witty nor funny and the fact that 80% of Rose's conversations with her peers are based on sexual innuendo doesn't help, just as the constant "slut shaming". Meads pretends to write a modern, sexually independent heroine but, in the end, it's always the same story of teenage girls accusing one another of being sluts because they (supposedly) had more than one partner. 
 In the end the story was gripping enough to make me want to read at least the second chapter, hoping in some character evolution.