First, let me tell you that wishing for this movie to be good will be of no avail. There's no reason in hoping for a satisfying thriller like this one seems to claim, because doing so will only lead to a massive letdown.
CAREFUL WHAT YOU WISH FOR's biggest flaw is neither its premise nor its narrative. There's a lot to negatively comment about those two areas, but they're still much more tolerable than the movie's horrible casting. None of the actors are able to serve the requirements of their roles, and while their characters hold promise of being interesting, none of the performers could actually pull them excellently, even to a tolerable level. Their dialogues and the overly familiar plot, are partly to blame, but it so difficult to jump to that part when the first thing that can be noticed is the horrible designation of the actors to roles utterly unsuited for them. There's this evil psychopath named Elliot who never really brings as much threat as he is required. Letting Isabel Lucas play a role that doesn't fit her age is perhaps the biggest mistake in the casting. Even with her capacity fully stretched, Lucas is never able to get halfway meeting all the demands of her character. Her character, Lena, is supposed to be a devious and cunning femme fatale, Isabel Lucas is plain boring. Almost the same can be said with Nick Jonas, although it's really hard to say his role's totally garbage, when almost half the time he's confused and waiting for a good line to throw. If it's any consolation, there's a lot of skin shown here, and I'm pretty sure Nick's fans as well as Isabel's will be pleased. Other than that, there's really nothing to expect.
It is really difficult to follow the narrative's flow when all that worries you is whether the characters are still going to be something interesting or not. The plot isn't new either, and it still could have been interesting, if the characters are played the way they're supposed to be. These flaws accrue to an overall feeling that is neither good nor okay, much less satisfying. Albeit cliché, CAREFUL WHAT YOU WISH FOR could have been an enjoyable experience. There is so much to mine in its premise, but its terrible casting paralyzes the movie and made itself incapable of digging such potential. The result is an overwhelming sense of dissatisfaction.