First and foremost, this film feels like someone went to their local grocery store, grabbed a random three-dollar mystery novel off the checkout shelf, and decided to make it a movie with some extremely popular and attractive people. In other words, it's a silly mystery movie with crazy, zany twists and turns.
Some of those twists and turns were easy enough to see coming, but some of them were straight out of left field. In addition to the entertaining twists, the film does a decent job of not taking itself seriously. The humor in the movie is peppered in during great moments. Some of it is cheesy, but if you're going to this film for a deep, thought-provoking film, don't.
The characters themselves are all extremely exaggerated. Lively's Emily is over-the-top sophisticated, crass, and private to the point where she won't allow pictures or even paintings of her face. Kendrick's Stephanie is bubbly, eager, awkward, and overly friendly. The rest of the cast fills in the needs around them, and while the cast is filled with one-note characters, they fulfill the needs well. Golding's Sean was my least favorite, but mainly because he doesn't have a defined archetype in a film filled with single-aspect characters.
The biggest issue with the film is the plot itself. Emily contradicts herself with the motive for her faking her own death. She tells Sean that she did it for him and for Nicky. Then she says she did it for her. On top of it all, she doesn't appear to have a plan to get the insurance money after it comes through. The film could have easily alleviated all of these issues with a quick scene or a line about fake passports for Emily and Nicky.
All in all, A Simple Favor is a fun romp filled with crazy twists and turns, humor, and great acting. Don't think too much about the film itself, and just go have some fun. It's definitely worth a getaway matinee.