I rode it a few years ago from the Samoen side, it’s pretty brutal. Took me an hour (the pros do it in half that). The worst bit it’s about half way in when the road ramps up to about 15% for What seems like hours but turns out to be only be about 1km. The horse flies at the top are pretty annoying as well.
The descent into Morzine seemed really steep and over in a matter of minutes. I’d recommend not heading straight onto the cat 1 climb to Avoriaz, I was seeing stars by the time I reached the top.
The Joux Verte climb (and descent) is great as well if you’re in the area. The col de Trechauffe is little known but really good as well.