The Boeing 747-8 has not been a terribly successful program. Boeing decided to update the 747 family with new engines and revisions to the wing along with a stretch to the fuselage. The resulting jet was delayed by its own and other program issues and it came around at a time when there were few passenger airlines interested and the freighter market was taking a kicking. The result has been anemic sales and a production rate that has steadily reduced as a result of the low demand. However, from a technical point of view, it is a nice upgrade.
The wing came in for a lot of attention and was significantly redesigned. The most conspicuous change is the introduction of the swept tips common to many Boeing designs these days. Less obvious is that the flap system was completely redesigned. The original 747 flaps, carried through on the 747-400 are very complex. Sections are triple slotted. The Boeing aerodynamicists came up with a single slot design to replace this which apparently has good performance but I imagine is a lot simpler to make and maintain. Only from the rear on approach can you see the difference. These shots compare a 747-400 from Air New Zealand with a Korean Air 747-8 and you can see for yourself how much simpler the new design is.