Ryan Reynolds as the star just doesn't work for me. When I saw him attached to the project, my reaction was "Really? That's too bad". Aside from him the cast looks pretty strong: Peter Sarsgaard, Tim Robbins, Mark Strong, Temeura Morrison, Jeffrey Rush (voice of Tomar Re). He just doesn't strike me as someone who can carry a movie like this on his own, and I wonder if he was the producer and director's first choice for the role. He's always come across as more of a smartass than anything else. And in the comedies that he has done that can work. On something like this? Hmmm.
Sounds like there were/are review embargoes until today (which is never a good sign I guess)
That is usually a strategy to keep the reviews from hurting the opening. IIRC, the movie opens on June 17th and we're 2 days away from that. The movie probably tested poorly and that may have prompted the embargo on the reviews.
I think a big part of the problem is that the DC properties may have a hard time competing with the Marvel properties. The DC characters have been around for a long time, but they have always lacked some of the grounding, reality and grit of some of the Marvel characters. And I think that's one of the big reasons why movie studios have only tried to tackle Batman and Superman up to this point in time. Jonah Hex might be a DC character, but I didn't get a sense that the film did all that well.