C
It suffered from the same problem as Doomsday: no heart.
And a lead with no charisma. This was basically just "Sinestro: The Movie". It's a recreation of Emerald Twilight with Sinestro and no Parallax. Every time he's on screen he just oozes menace and coolness. He just dominates this film, and that's not a bad thing.
Hal is just a big, boring, blah with nothing there. Coma-inducing doesn't even begin to describe him. It's no wonder they cast someone as cool and exciting as Ryan Reynolds to play him. If they wanted an authentic comic book version most of the audience would be asleep half-way through. They got rid of most of his backstory and exposition in order to move the plot along. On one had, it's a good thing because it gets right into the action. On the other hand, there's nothing there to relate to and empathize with character-wise. Sinestro at least has proper motivation. You actually give a shit about him. Hal could have been killed off half-way through and no one would notice. All the Green Lantern revamps they've done recently could have easily been done with Jon Stewart or Kyle Rayner in the lead. If there's anything holding that franchise back, it's their choice of lead character.