Just read the synopsis. I didn't think it was that bad. For a follow-on to SR at least they tried to make the events in the movie have lasting consequences. I'm not sure about a Kryptonite moon. I agree with one of the other posters that that might have an adverse affect on Superman, especially if he flies into space anywhere near it. It might've made more sense to just have the Brainiac ship encounter the floating island and trace the trajectory back to Earth.
I do like the inclusion of Brainiac and I also like the clash in approaches. That would be neat to see. Though Superman IV was horrid regarding production values, a good deal of the story, and even most of the acting, the basic idea I always liked. And this is similar. However I find it unrealistic that the world would just so easily agree with Brainiac or turn against Superman, though it would be neat if there was lingering doubts about Supes based on him leaving after Superman II. But I liked the idea of the cloned bodies.
I've heard something similar on this board and others about Jason's fate if Brainiac was involved. I would be shocked to see if they actually would've killed him off, though I wouldn't have minded tying up that loose end. I wonder how Lois and Clark's relationship was in the film? The synopsis doesn't touch on that, or how Lois would react to Clark killing their son? If Lois became his enemy in a SR III, that might've been an interesting storyline twist, minus the limp acting of Kate Bosworth.