Many will agree, many will disagree. But from the view of an actual K-pop fan, seeing PSY's video for the first time was refreshing. It differs so much from other K-pop songs and has opened up the wonderful genre to the entire world. You may be sick of it at this point, which is understandable, but it's obvious that "Gangnam Style" made the biggest splash in the music industry this year.
Honestly, I don't really listen to music, I don't know why. I play music, but don't listen to it.
As for the best song of 2012, I don't have one, but I have to agree with Majora's Cat. I hate Gangnam Style, but on behalf of more or less everyone I know, I have to say Gangnam Style was along the lines of best music of 2012.
An excellent rap song about alcoholism; he laces his story from beginning to end flawlessly - from his former experience with others who drank, to the peer pressure that caused it, then to his conscious telling him he needs to stop. This is how rap should be.
These guys aren't very well-known, but their music is incredible and these are two of the best songs I've heard. They have a style reminiscent of Linkin Park, so I highly recommend checking them out if you like Linkin Park or just rock music in general.