I have to say I really don't think this is one of the better big screen comic incarnations of late but while I don't think the source material or the underlying story of the film is the problem in the case of Green Lantern I think where it does go wrong is in the casting and the direction.
Everything here just seems tonally off, as if the cast are running around in a different film than director Martin Campbell is trying to make. Ryan Reynolds is fine as a comedic actor but he doesn't do very well here when trying to emote or have any depth to Hal Jordan's storyline and Blake Lively is horribly miscast as his love interest Carol Ferris. Even the normally reliable Peter Saarsgard and Tim Robbins just don't work well.
Add in a structure that has us leaping all over the place between Earth and the world of the Lantern's and the film soon becomes a tiresome mess that is barely saved by the presence of tens of millions of dollars of visual effects money and for sure it's glossy and beautifully done on Blu-ray. But that's no big achievement these days on big scale films designed for the format. I'm glad I watched it out of curiosity, but I'll never watch it again.