The song was titled "Baby Blue":
baby blue is arguably the greatest power pop song of all time; aimee mann's version is, to my ears, even better than the original. i just read that according to billboard, after the breaking bad finale, streams of the song increased by 9000% and that the song entered into the top ten on itunes. anyone interested in the band should read their bio "without you," which damn near breaks your heart.
My first reaction was reflected in the Rolling Stone article linked above:
The song was really kind to the character because it intimates that, despite all of Walt's horrific behavior, he was always just a chemist at heart. I thought it was a deliberate choice to ignore the "He had it coming lyrics" in favor of "He made his own choices". I neither felt bad for Walt, nor good that justice was done - either of which might have been what I expected. In a weird way, it struck me as a happy ending for the show.