There wasn't enough "plot" to fill 102 episodes and keep the viewers engaged. The last 5 episodes were painfully slow, they felt like eternity. Jang Jin Gook must be one of the poorest written characters out there. The relationships between all of the 6 leads were just bad. I don't ask from such dramas to be believable (they're never meant to be) but there's a certain limit of blatant stupidity shouldn't be crossed unless you are making a mobbit show.