Its kind of a shame that he plead guilty to this, I believe if you are charged with a crime you should always fight it with a lawyer. In this case I suspect he didn't have the funds to defend himself which is sad.
As for the punishment, five year sentence and a quarter million dollar fine seems like a lot, but to my thinking that depends on the amount of money he made from it. If he makes an income from piracy that seems like it should be a crime, with a sentence, but if he was just a member of a file sharing scene (which this sounds like it was) than I think it should be much less. The difference being that if he makes money selling what an artist makes without giving the artist his fair portion of the proceeds then he has effectually robbed the artist of confirmed sales. If he is just freely making the music that others have shared with him available he may actually be encouraging people to purchase that music.