Hi Jan and Pelerina,
I'd say Gronze is pretty much spot on. Most of the walking is straightforward, but a couple of stages have sections with narrow steep paths which are wilder than what you'd normally expect on the camino.
Firstly the stretch between Cicera and Lebena - hard yards but delightful.
And secondly the section after Potes up to either Espinama or Fuente De (in my case). Here the road, hogs the easy route up the valley, so the camino path jumps off at intervals into detours (often steeply) up the side of hills that bring you back down to the same road again. About halfway along I decided that leaving the road (and often getting lost due to poor signage) was a mug's game and just stuck with the road, which was fine. Actually I arrived in Espinama much earlier than expected, suprised at how easy the road was. If I did it again I'd just consult
Mapy.cz and either do all the off-road detours or select a few, depending on how energetic I was feeling. In fact I recommend looking at this section on
Mapy.cz (select outdoor map) now, and you'll see exactly what I mean. I think this is the section Gronze is referring to when it says
The harshness focuses on the Cantabrian stages, especially if you follow the marked itinerary (as it should be) avoiding the roads
For the section up to the highest point (from Fuente De in my case) you just follow a wide track used by the local 4x4 vehicle club which winds gently up and up to the highest point. There you follow the signage on an easy path for about 2.5km until you hit the tarmac road. Then you have a long descent along the road to Portilla de la Reina. And that's it really - all the rest of the Gronze stages to Leon have only one or two stars of difficulty.