This may be stating the obvious, but hiring the right director for a blockbuster movie is a key factor in making it a success. The reason that this point needs to be reinforced is because in today's era of franchise filmmaking, you often get the feeling that the person behind the camera isn't always the one calling the shots.
The most expensive movies are sold on the strength of the brand and popularity of the characters, not the actors wearing the costumes or people yelling 'action' from behind a monitor. As Gareth Edwards, David Ayer, Joss Whedon and others have found out in recent years, the studio will release their version of your movie into theaters, and there's nothing you can do it about it.
Maybe this is part of the reason why the studios are now recruiting relatively inexperienced directors straight from independent cinema or commercials and putting them in charge of mega-budget productions, in the hope that they'll be more willing to work with constraints and compromise. Yet, for every Colin Trevorrow or Joe and Anthony Russo that make it seem like a good idea, there's a Josh Trank or Carl Rinsch to provide the counter-argument.
Blockbuster movies in general are becoming more homogenized and familiar on an annual basis, meticulously designed to appeal to everyone and offend no-one. Studios need to take more chances on directors that could actually do something exciting with the material because the safer they play it, the less people are going to care.