Just watched this. I would recommend it to all Green Lantern fans. Good story lines, especially since they deal with other GL's besides Hal Jordan. Mogo once again proves that yes, size does matter. lol  The only drawback that I saw to this movie was the timeline. Someone did post the Blackest Night error but this is dealing with the apparent time that Jordan has been a GL. Based on First Flight, we are led to believe that Jordan was not long on the Corps, as in still a rookie, before defeating Sinestro and Arisa was already a GL. In Emerald Knights, Jordan seems to be fully trained and integrated into the Corps as though he has been there for many months and Arisa is brand new.  Perhaps there was some hidden time warp in First Flight that I missed. You tell me. 
 
Compared to First Flight, there is also a bit more violence. While we accept that GL's may have to kill in self defence, this goes a bit overboard, as in the Titanic hit a small chunk of ice. Somehow, I just don't think GL's would be quite so mercenary. One other bit, we do get the story of how the Guardian's created the first four rings to combat chaos and create order in the very beginning. Seems like the Manhunters did not exist since they came before the rings, right? Yet Jordan promises to tell Arisa about his fight with the Manhunters. Another time warp perhaps?  
 
Without giving away too much, Krona is the main villian here, and his shadow demons from the "Crisis". There is only a little bit of a back story here that cried out - "Hey, don't forget the Anti Monitor" but no such luck. 

The Good : Nice to see alien lanterns given a turn. Nice tie ins to what's to come. Plus I finally know how to pronounce Atrocitus 
The Bad : Nothing really. The aforementioned time difference with First Flight and Emerald Knights does not distract from the story unless you really want to be anal about it. Sinestro's voice over is a tad bit too "English", not to knock you blokes
The Ugly: Why has it taken so long for DC to make these movies? True, they could be better but GL would have been nice a few years ago when SUperman and Batman animated shows were riding high. It would make a decent (if well written) animated series of its own.
 
All in all : Worth the purchase. Go out and buy it Poozer!