Every March Hollywood thrusts forward a summer blockbuster that is neither summer nor blockbuster. It has a habit of being directed by Zack Snyder and always contains overly heavy CGI. This year, that film is John Carter. It is also a $250-million risk, and this adaptation of old Edgar Rice Burroughs pulp novels has a great deal of potential energy for backfiring. The fact that the film is repetitive and not particularly eye-catching