I've flown Nadi to Seoul on Korean in J. The service was exceptional and the food very good, however the seating was terrible. In fairness, it was a "regional" A330, however the seat was somewhere between the Qantas domestic J and old intl 767 J.
PTV was a tiny screen with poor selection on a loop and sleeping was virtually impossible. The crew nearly made up for it, to the extent that (if it were a daytime flight) I'd consider using them, however if you intend to get some rest its not worth is.
As mentioned, given the very competitive business fares being offered at the moment, there are better options. One plus though is a free overnight stay at the Hyatt in Incheon if you're connecting onto a Euro-bound flight.