we took a touring caravan in summer 2007 and deliberatley stayed away from from playa joel, although we did visit it to make sure we had made the right decision - and for us it was!
This site is enourmous with a very lively late night feeling ( I would thing teenagers love it !). we felt all the pitches were very small and extemely close together.
However - good shops, direct access to beautiful beach , walking distace to the town and lots of entertainment and huge playarea for the kids- if you want lively this is the place for you.
we stayed in the stunning playa de omybre area about an hour from santander in the opposite direction to noja.
Overall the weather was good but extremely changeable ,so a little frustrating at times- just get to the beach - clouds, go shopping or site seeing because of poor weather and the sun comes out !!!! But not so hot that it's unbearable - just right for the age of your children.
Whole area had beautiful beaches but be sure to take a phrase book when out and about most still don't speak alot of English
good luck and happy hols