Karms,
I just finished my Camino Norte which I walked from Hendaya to Colunga.
As I did the Frances last year I can compare the two and the aspects that I can compare:
1) Norte is much,much more beautiful than the Frances: some parts you walk along the cliffs with on your right the sea and on the left the mountains.
2) Norte is more challenging: it is a lot heavier and tougher to walk because of the continious up and downs. Most little villages you cross are at sea-level so after your coffe-break you know one thing for sure......you have to climb again.
3) Norte has much fewer refugios and as I experienced... alot of them were not open in May. You have to think/find out about this before starting an etappe otherwise you have to make a lot of kilometers.
4) You do not meet a lot of other pelgrims (in May) as on the Frances. That will give another spirit along your route: if you did not do the Frances I would advise to do that first.
5) Some parts of the Norte are not nice: esp. the great cities as Santander and Bilbao are no fun to walk. At some stretches you walk along the N-632 for some km adn sometimes this is boring and not nice.
See the picture-index with some pictures of mine of the Camino Norte.
Buen Camino!
Paul