One more thing, Green Lantern is not weak against the color yellow! That's like saying fire is weak against water because it's blue (bad analogy I know, but I can't think of a better one at the moment).
What I didn't get was how calmly Hal reacted to learning about aliens. Most people, I expect, would freak out. But, he took it in stride. Almost like it was an everyday occurrence. Honestly though, I think I would react the same. I mean come on, thinking we are the only ones in the universe is just arrogant.