I live just round the corner really from Santander just outside San Sebastian. It depends what you want. The culture and general style of living here is fantastic. The winters I've seen can be a bit grim, wet and cold but then you get spring in Feb and it's a glorius spring. Warm but with the odd storm. Then summer has been fantastic. Just now I can feel the nights are getting a bit colder but it's 30degs outside today. Summer will hopefully last until the end of October. I can't remember a day I couldnt' ride my bike with pleasure. I've not worn a jumper or a jacket since late Feb / early march. San Sebastian, Biarritz etc are all within easy reach and they're cool cities. The beaches are breathtaking and can be quite and peaceful or dangerous and wild depending on the weather and location. That goes for the women too if that sort of thing interests you!
The hills are amazing here and it's the thing I instantly miss when I go elsewhere in Spain. We live 5 mins from the beach but are IN the hills, there's the odd flat bit of ground but apart from that it's hill after hill after hill. The riding (I think) is absolutely fantastic. Big climbs and great descents. Recently I've had people come from all over spain to ride some trails I've found (via a Spanish MTB forum) and they raved about it here too.
Downsides? Well it's expensive to buy houses here. Also people don't speak a lot of English as they have the Spanish, French and Basque to contend with. There's not much multi-culturalism so it's hard to find a good pizza, curry, thai etc etc which I took for granted living in Glasgow. The beer is rubbish but the Sidre is a thing of natural beauty. Rioja is a stones throw away too!
Anyway, I go on a bit. Had some vino with lunch too! I love it here and although I miss Scotland I like it much more here.
No doubt Markem will be along too because he loves it here as well!
Drop me a mail if you want to ask any questions. I think mails in my profile.