Also, while comics fans are just waiting for Sinestro to betray Hal, they managed to genuinely surprise me with the secondary villain. That's a nice way to include something genuinely unexpected in the narrative (though I suppose you would object if you were a big fan of Boodikka).
Narratively, my one real complaint is the very unclear climax; after Sinestro drains the battery, Hal starts hammering away at the 'green element' trying to get it to do something. Then it starts glowing green again and basically turns him into Ion (the embodiment of willpower, in the comics held by characters like Kyle Rayner and Sodom Yat), though none of this is explained.
Given Geoff Johns' extended stay on the comics title recently, and the way so many readers describe it as "definitive", there's quite a lot of this that goes against Johns' take on the character (Timm and co, of course, having grown up with other comics). The Guardians of the Universe all have names, for example, and distinct personalities (one of my favourite parts was Ganthet and co. sadly looking on as a rain of rings descends on Oa after Sinestro disables the battery, which kills every Lantern currently out in space, engaged in combat, etc.). The GL rings and Sinestro's eventual Qwardian ring are fueled by green/yellow "elements" (big glowing crystals) that power the batteries.