I was a huge proponent of this movie from the time it was announced. Hal had long been one of my favorite characters, as his "Chuck Yeager" sensibility really appealed to me.
That said, I was horribly disappointed by the Green Lantern movie. Why? I'll tell you.
The script had some serious pacing problems. There was the obligatory "secret origins" sequence showcasing the death of Martin Jordan, which is fine, but there was very little time spent on making the audience care about the character of Hal. There are some nice moments with his nephew, but other than that, he seems like a rather generic cutout in the frat boy, "Top Gun" mold. This gives the audience nothing to really root for as the movie progresses.
The Oa sequences, which were by far the most visually spectacular portion of the movie, were poorly handled. WB spent an inordinate amount of time and money marketing the various Green Lantern Corps members only to reward them with perhaps a few seconds of screen time apiece (Kilowog being the lone exception). Again, this creates no emotional investment on the part of the audience, which means that when several of these characters bite the proverbial bullet at the end of the second act, there is no reason for the audience to care.
Martin Campbell deserves much of the fault for the critical failure of this film. All of the actors in the cast, from Ryan Reynolds on down, have all turned in far superior work from an acting standpoint on other films. Ryan Reynolds was allowed to slip, far too often, into his standard personality, which is completely on the director. His Hector Hammond was overblown, and many of the supporting characters felt like cartoons rather than fleshed out people. Again, when you know that the actors have the capability based on previous work, then the responsibility for this failure falls squarely on the shoulders of the director.
3) Wasted Opportunities
Parallax: Done. Hector Hammond: Done. Krona: Done. All great concepts that could carry films on their own, if done right, and were mashed together in an unintelligible jumble.
The original production design for the film included references to Gotham and Metropolis, which would have made this film feel a part of a larger universe, but was written out by WB execs as "confusing". There was even an Alan Scott reference in the original shooting script that was also canned.
In short, the production was rushed, the script was rewritten to death, and the studio didn't trust audiences to be intelligent enough to know a good movie when they saw it. The sequel has the opportunity to make up for a lot of these mistakes, but only if done right. Otherwise, WB will have squandered one of their best opportunities for an enduring science fiction franchise that could be the next Star Wars.