I am cautiously optimistic here. The big cast photo did not inspire me but the trailer that came out of SDCC has turned me around, rather.
For one thing Margot Robbie's Harley Quinn looks so much better as a performance than as a static image. She injects a huge amount of manic personality into the role that goes straight to that “I exist to amuse myself and the whole rest of the world is just a playground” place that my favourite versions of Harley inhabit. Will Smith is clearly very engaged in the chosen scenes. Most of all, though, Jared Leto's Joker persona is much better than the design foisted upon him. He's a straight-up sadist and there is a cold whimsy to how he delivers his lines, like a tired comedian who has come to view their own material as chore to get over with.
I just wish that DC-Warner didn't feel the need to include a scene that all but screams “LOOK! WE PROMISE YOU BATMAN IF YOU JUST COME AND WATCH THIS FILM!”. It speaks to a (admittedly not unjustified) lack of confidence in the product.
The Fantastic Four reboot still looks really rubbish, though.