In the movie you've Wonder Woman getting all teared eyed with the WWI pic, a gift from Batman, and then writing an e-mail to him full of affection, which is weird because the movie kinda feel like is trying to force two romances at the same time, and then in the flashback proper the movie goes out of its way to show how hot Steve is and how thirsty Diana is for him. You've Chris Pine naked, Diana fondling his junk, Diana constantly giving him heated gaze, Steve constantly manhandling Diana and Diana getting visible wet by it. Heck, throughout the entire movie Steve acts pretty much like a dad teaching his retarded daughter how to behave and be a proper lady.
So if there's anything that critics will launch against, it's probably that. You already see people complaining about the "heteronormative" stuffs in their reactions.