Only stayed in one hostel so far in Seoul.

I read a LOT about them before I booked mine though. I think its more to do with, what you're looking for in your accomodation. Party atmosphere vs Serene and quiet is one of the main contrasts i've seen from reviews.

I stayed at Fully House. It falls into the latter category. Out of the way, its not in the hongdae area and the style of accomodation was very apartment like. Everything was private rooms. There is a common area, but its on a seperate floor, you don't have have to go through it to your own room so its usually very empty.

Was awesome for what we were looking for though. Room was more than adequate. Super private. no shared showers. Was like living in your own apartment.