That there might be < GASP! > something cerebral in it, that isn't in keeping with the usual punch-em-up.
WHile I have not been digging around for them, the typical negative review I've seen is that the movie basically takes what emotional depth it might have had, and replaces it with Grimdark and lots of smashing things up - basically, putting a grey and brown filter on the four color, and hoping that makes it *look* cerebral, without actually having intelligent content.
For example, one review I saw:
"'Batman v Superman' is an overlong, boring, masochistic, mess of a film that fetishizes violence, makes no sense, and is full of bad acting and distracting CGI. Who would've expected that from Zack Snyder, director of 300, Watchmen, Sucker Punch, and Man of Steel? Thankfully, it also includes Batman's origin story, which is great because no one's ever heard that before."
And a friend of mine commented: "Best line I've seen from a BvS review: "I left feeling like I’d just been yelled at by someone I don’t know on a bus."