Definitely one of the weakest episodes. The particular story of McGarrett and his girlfriend as a two-man invasion team feels more like cheap filler than anything else.
It has nothing to do with the task-force, but more with McGarrett's SEAL past yet the question of what McGarrett has to do with North Korea is baffling as there's no historical background to go with that (sorry, but McGarrett wasn't even born for the Korean war).
For some reason, a SEAL team violated the territory of a sovereign nation, lost a man while retrieving an arms dealer ("why" is beyond logic as North Korea is a black hole for arms dealers, you simply can't do business given the embargoes and communication restrictions - any arms dealer in person there is essentially neutralized).
McGarrett goes back to once again violate Korean borders (both ways since he doesn't even have the consent of the South Korean government either, but since when do Americans need that?) to retrieve the body of his mate, risking his girlfriend's life in the process.
Even more senseless is the cold-blooded killing of an incapacitated enemy. After 10 years since the initial events, McGarrett holds a grudge against a man who's only fault is to have defended his own country, on his own territory and having followed his commander's orders.
This episode is a huge stain on McGarrett's character.