It is fantastic - watch out for the one the pros call Col-de-Bugger-Me
I did it. Probably the slowest I have ridden up a hill since Bwlch-y-Groes 300km into the Cambrian 4C. The 4 consecutive km above 10% in full sunshine and no wind were fairly stupendous. The closed cafe at the top somewhat less so. But there was also the 10km to the summit of Errozate from south of Ecumberry, which averaged 9.6% and the Col de la Hourcette with pretty much the same profile, and then the D428 Route Napoleon straight south out of St Jean Pied de Port, where the only relief is the almost static trekkers on the Camino Frances.
Rode 6 days out of 7, with 4 100km+ days and 2 100mile+ days, and on the day off drove up to Col de la Pierre St Martin and hiked, scrambled and properly mountaineered to the top of Pic d'Anie (2504m).
Twice saw Pine Martens and on the first day sat and watched Golden Eagles circling above my head. I may well go back again next year - probably the most beautiful roads I have ever cycled on. And I only rode 3 of the 4 possible ways up to the Col d'Iraty / Col Bagargi - it has different names from different sides - and Port Larrau was closed (I presume for roadworks) - so there are a couple of fantastic France/Spain routes untouched. And the Grand Pression Blonde Eguzki is perfect after a hard and hot day's ride.