I've been trying to think of the proper perspective for this route, surely one of the most beautiful and interesting courses you'll see this year. Using the Giro, which I know much better, I first compared it to the Montevergine stage, in that it's a somewhat isolated stage for the GC guys at the start of a grand tour. But the Montevergine climb is far less selective, and the stage leading up to the climb was somewhat of a leisurely tour around Amalfi. Today's stage in Asturias will be tough from the get-go, albeit in the form of rollers and small climbs before the main event.
The climb to the Lagos does resemble (statistically) the tenth stage of the Giro, to the Santuario Nostra Signora Della Guardia. That stage was 9km averaging 7.8%, with a max of 14% near the top. Today's climb to the Lagos is slightly longer (12km) and gentler (7.3%), but just.
Of course, every road is unique, but assuming the comparison holds, the top dozen riders to the Santuario were all within a minute of each other, so the Vuelta probably won't be won or lost today, at least not by anybody who had an actual chance. The gaps could go out a tad more, because the course should tire people out before hitting the climb, but ultimately this will be a stage to entertain the fans and to help shake out the list of contenders. That is about it. So enjoy, it's going to be a visual feast and some damn fine racing.