Question: "Can a great show come from the man who wrote X-Men: The Last Stand?"
Answer: No.
And thus concludes another installment of Do You Really Need to Ask?
"up-and-coming scifi screenwriter"? What PR flack paid you to write that? Spaiht wrote one of the most mind-numbingly bad scripts I've ever read, SHADOW 19. If he's writing this, it doesn't bode well.
I honestly don't have high hopes for this movie. Ryan Reynolds isn't the worst choice for Hal but neither is he the best choice. He's a milquetoast choice if anything -- he doesn't have the presence or depth of a Robert Downey Jr., but then again, neither is he woefully miscast like Ben Affleck as Daredevil. No, the problem with this film is that the script is hacky, and Martin Campbell is merely looking for a huge payday. But we live in the post-Transformers 2 era now, and that means movies don't have to be good. They just have to be big.
It's not that I think the movie "sucked" -- I rather enjoyed it, actually, and people that say it sucked are out of their minds -- but I would definitely say that it "lacked". Specifically, any kind of coherent theme: this was nothing but a straightforward popcorn flick without any depth. And that's disappointing because there were numerous opportunities to weave a great theme (destiny) into the action of this film, especially considering the reliance on the time travel trope.
I don't think the danger in Flash Forward sucking is as much from the concept of resetting it at the beginning of every season so much as from the fact that Brannon Braga is on the show.