I was on the premium economy seat to Tokyo for night flight, and wanted to see the differences, I booked for economy seat for morning flight to KUL from Tokyo and frankly speaking, it was as satisfied as the premium seat!
Although the seat was different and there was no extra amenities, the space was still big compared to other airlines economy seat (it was rated world first class economy seat) and one thing I couldn't forget is how amazing the meal was and we were given a cup of Haagen Dazs ice cream for dessert! Imagine when you finished your meal and expected nothing else but then you were given a cup of ice cream and everyone loves ice cream! I was enjoying the whole flight that I watched a few movies rather than taking naps till we reached KUL.
Certainly choosing this airline again for my next trip to Japan!