In my humble opinion... A real blockbuster? One that makes a shit-ton of MONEY?
1) It's gotta be HUGE. The bigger the better. Why? Because the more a studio spends on a movie? The more publicity it gets. The more discussion it gets online. The more anticipation is developed. In fact? I honestly believe this can easily become part of your marketing protocol.
2) You need both famous actors and extremely talented actors but in reality? I don't actually think you need to have the MOST FAMOUS or the most expensive. In fact? I would find a happy medium here... A famous actor but one who's rate is reasonable. Not a $25 Million Dollar behemoth with net points. I actually hate this but I do think it's absolutely true. Great character actors make famous actors look great. I believe combining the correct mixture of both in a movie is another piece of the formula.
3) Keep the story simple. Unless you're a Christopher Nolan? Probably best to keep the story simple so anyone and everyone across the globe understands it. They used to call them FOUR QUADRANT FILMS -- maybe they still do. But today? An audience in China needs to be able to understand the story as easily as a an audience member here in America. I think to do that is not that difficult as long as you stick to the basics of humanity that resonate with ALL OF US. LOVE. HATE. REVENGE. Yada yada. You know the drill.
4) Your characters need to have flaws... At least the MAIN characters. Anyone and everyone can identify with an EVERY MAN or EVERY WOMAN. They should not be perfect. You want your audience to immediately be able to jump on their train and ride with them all the way through the story.
5) Great music. Exciting music. Music that goes WITH the story and the action of the story.
6) I can't say I know WHEN to actually release a film but I am damn sure that a film you want to become a BLOCKBUSTER needs to be released at JUST THE RIGHT TIME. Unfortunately, for us mere mortals? All we can do is what we can do. Studios however, have access to data that they can crunch for weeks on end to nail down a profitable release date.
Of course these are just broad strokes... But in my humble opinion? You need all of this to really generate a BLOCKBUSTER.
Worth reading...