Manganiello's got the build down, that is for sure. I just hope his acting skills are decent. I've seen too much of dull-faced Manganiello in the movies, but I'm still willing to give him the benefit of doubt.
As far as the movie goes, I'm positive it's gonna kick ass. Affleck's been in two DCEU movies which missed their marks. He obviously cares about the characters, the universe's well being. Not to mention he has mad directing skills. I just want, and god I can't even stress this enough, a comics Deathstroke. Not the pushover portrayed in Arrow, Son of Batman or Arkham Origins/Knight. Obviously, they're gonna have to tone him down a bit, since comics Deathstroke actually took down the entire Justice League (albeit a Justice League that was mostly comprised of D-B listers) but I still don't want him to be thrown under the bus for the sake of plot advancement.