I agree with those who said it ended too cleanly. Its possible that they had it all animated before a 2nd season was green lighted which explains the whole tie up all the loose ends bit. I also agree with everyone who doesn't think Korra should've ended up with Mako. The guy was clearly infatuated with Asami for several episodes and there didn't seem to be much lead in to him liking Korra just suddenly BOOM he's all up for protecting her over Asami. I'd rather she got over him and moved on with her life. I feel sorry for Asami now
WHAT THE HELL WAS IROH THINKING?!?! Seriously, sending an uncoded message over open radio waves when you know the enemy has a high-class techy under their charge? YOU SHAME IROH'S NAME! Iroh was badass, you sir are an idiot. I was expecting him to be all like "Psyche, you think I'm THAT stupid? He's not there, He's at another position and will move in X hours." but no he was just that stupid.
I enjoyed the series as a whole but wish they'd kept Amon around. The guy was the biggest threat to the Avatar we've seen and even defeated her 3/4s of the way. Up until the spirit ending I was fully expecting season 2 to be a search for Amon to learn the secrets of how he removed the bending.
The explanation for taking away bending was brilliant. Somehow he moves the blood in the brain in such a way that breaks the connection in a bender's mind to the elements. The biology is still there in the bender to be a bender but the connection to the spritual energy does not. Since the Avatar us an energy bender, however, she can break and restore these connections at will, at least in Avatar state.
In conclusion: Brilliant series! I only hope they keep it up for season 2.