For those that complain about cannon and mythos: which are you talking about? Comics have, for some time, banked on "multi-dimensional" story branching (i.e. kind of lazy retelling--reselling--mechanic). So why can't you accept that this movie is a new dimensional branch in the cannon? Because you can't hold it and turn pages?
I've seen some serious love for the Injustice branch, and while it has a comicbook companion, it is mainly a videogame, yet I've seen no one screaming about destroying cannon over it.
I think you've completely missed the point of seeming a movie if story element differences ruin the experience for you. You have to go in with as-near-zero expectations as you can.