There are two main characters in this story, Gerald and Jessie. As Gerald, Bruce Greenwood (Star Trek) creates an interesting character that is hard to judge at times and has some depth throughout the whole film. As Jessie, I found that Carla Gugino's (Night at the Museum, Watchmen, Sin City) performance was too exaggerated. In the situations that she is put through, I don't think that anyone would have reacted in the same way that her character does. Certain parts of her role are believable, but the first half of the film feels overacted.
Overall, Gerald's Game has ideas that are hard to figure out at first. The ending has twists that are not easily resolved through a first viewing. I'm glad with some of the choices that Flanagan executed in his direction, but there is some CGI that is inexplicably bad. I understand that the film would be a complete bore without some of the horror conventions used, but I wish that more of the budget was spent on them. This is the first Mike Flanagan film that I've seen and I believe he still has some potential for growth as a horror filmmaker.
The Bottom Line: Don't expect to be jumping out of your chair throughout the film, but there are some ideas that might keep you awake at night pondering.