Entertainment Weekly: There’s a smugness in his performance that only appeared around the edges in Dawn of Justice. Now it’s the whole show. When Affleck’s Bruce Wayne heads off to convince Jason Momoa’s Aquaman to enlist, he wisecracks, “I hear you talk to fish…” with a cocky, condescending grin on his mug. At that moment, Affleck looks like the highest-paid captive in a hostage video. Fortunately, there are other actors who look like they actually want to be there.
Hollywood Reporter: Ben Affleck, donning the bat suit for the second time, looks like he’d rather be almost anywhere else but here; his eyes and body language make it clear that he’s just not into it.
GamesRadar: Affleck appears to have mentally checked out of the role already.
The Guardian: Affleck spreads a pall of dullness over the film. He doesn’t have the implacable, steely ferocity and conviction that Christian Bale had; he seems to have a faint sheen of sweat, as if the Batcave thermostat is up too high, and his attempts at droll humour and older-generation wisdom make his Batman look stately and marginal. Maybe we should get George Clooney back for the role.
IndieWire: Ben Affleck, still just one frozen stare away from being an actual statue
Screen Crush: Affleck’s Batman is the closest thing this movie has to a main character; he drives all the action and anchors all of the group dialogue scenes. And I mean he anchors them, dragging them down with his sullen, one-note line readings.
New York Times: Having seen trouble on the horizon, Batman, a.k.a. Bruce Wayne — played with a sepulchral growl and bespoke stubble by Ben Affleck — takes the lead on this enterprise. He’s the insistent manager as well as the scowling host, the guy with the cool digs, smooth rides with blinking screens (“critical damage” reads one with great comic-book sincerity) and suave butler (Jeremy Irons as Alfred). He’s also pretty much a yawn. […] Affleck, a generally appealing actor who can plumb the depths when pushed (“Gone Girl”), needs something more substantial (or just more jokes) if his Batman is ever going to work.
Business Insider: Ben Affleck looks to be over playing Batman. He gives a flat performance.