It's tolerable but I wouldn't get too excited. The seats don't go flat which will most likely mess up your back when you try and sleep and be careful with tight connections as there's a good chance that you and/or your luggage might not make the flight.

Ironically the thing that I find best about KLM is that because of the lack of comfort and also the flight times (which see you spat out into Asia at 2:45am UK time) that I suffer less from jet-lag when I fly with them as I will maybe have had a couple of hours sleep on the flight which is just enough to see me through the day once I arrive but I will be ready for bed by bed-time.