Personally speaking I dislike the Col de la Cayolle. It's bumpy, unnecessarily narrow, and the old wrought iron crash barriers appear especially designed to slice sliding bikers into pretty shapes. Much of it is a country ride rather than an alpine pass.
From Guillaumes the road is pretty busy and uninteresting until you start the climb from about St. Martin d'Entraunes where the road just gets bumpier as it gets higher. Tree-clad it's fairly narrow but with good visibility.
Towards Barcelonnette the ride becomes more interesting as you pass high up along the Gorges du Bachelard, and then pass down rapidly into the narrow and long gorge below. There are a number of sudden 90? turns over narrow bridges to put a stop to any rhythm you may have got going. The scenery is superb, but ultimately can't make up for the terrible road surface. One of our least favourite passes.