This is one of the biggests urban beaches in Spain. It's great to have a long walk or ride a bike. Even though restaurants and bars by the beach are very tourist and there's a lot of people around there, I think the sunset worths it.
That is true, a bit too much mass tourism for me!! Better Triana, my favourite artist café Sonata (c/ perojo, 32), my favourite shops (Mango, Desigual, Charol) and my favourite theatres (teatro Cuyas y teatro Pérez Galdós).
I'd say most people in Las Canteras arer actually locals, though there are always some tourists thrown into the mix. Still, "quiet" it isn't.