I went to a wedding there about 2 years ago and stayed for about 4 days. I loved it. It's a very relaxed city. It struck me as less cosmopolitan than Barcelona but this was one of the things I liked about it - the shops still closed at lunch, if you went out for a drink in the evening the bars were full of spaniards etc. The Old city is very pretty and the beach was nice enough. We didn't make it to the Aquariam but others in the wedding party did and said it was spectacular. I'd definitely give Valencia the thumbs up.
Gnash