The apartment is well located on the 14th floor overlooking the opera house - a really good view of this interesting part of the city. The park, Science museum and Oceanografic are easily walkable - we had a couple of nice walks from the apartment through the park and up through into the city centre. The bus stop directly outside the apartment (€1.50 - pay cash on the bus) linked directly to the centre of the city, and also to the beach/harbour area. Parking at the apartment (underground parking with tight corners and lots of pillars!) was convenient - but you only really need a car if you're planning on getting out of the city. There are some good restaurants nearby 5 mins walk away (we particularly liked La Mafia). Inside the apartment is spacious and clean. The kitchen has all you need to make a simple meal, and the bathrooms were fine. You'll need to buy some shampoo/shower gel as the amount provided was minimal - but the supermarket nearby was 5 mins walk. Sandra met us and showed us round, and also provided a map of the area with some helpful hints about where to go, including the supermarkets.
The balcony is relatively small, but with good views and was a nice place to sit in the evening. If you have small children, you would need to watch them carefully as it's high up!
The outdoor pool area was small and always packed with children and their parents, so we didn't use it. It would be fine if that was what you wanted - but we would have preferred it to be quieter!
We made use of the sofa bed during our stay, which was a comfortable double. The air conditioning was also effective and welcomed!
Valencia itself is a good city to explore for a few days - some interesting museums/galleries. We particularly enjoyed the Centre Arqueologic de l'Almonia just behind the cathedral - remains of the Roman settlement in Valencia. The beach area was also a good contrast to the older parts of the city. We went on an excursion to Sagunto - about 30 min drive. The town itself is unremarkable, but the roman theatre and ruined castle are impressive in their scale (but be prepared to walk up some steep hills to them!).
We would definitely recommend Alberto's apartment if you're visiting the city - particularly if you want somewhere slightly out of the main city area, but still with some interesting sights and restaurants nearby as well as easy access to both the city centre and the beach.