This is actually really bad. If it was just some random kid who hacked then the 9/11-style threats would have just been probably a joke to try and scare people, but if it's actually the Government of North Korea who did it then they were probably serious about the threats.
I don't know why people are surprised, any country of reasonable size could hack into a company like Sony with government funding and support. North Korea will collapse eventually, we just have to hope they don't do anything serious before then.