We were there for a day whilst on a cruise. I liked it.
Running through the middle of the city is long and widish green park, which is rather pleasant, and may help you get around if you hired bikes. It stretches almost all the whole length of the city. You can see it on any map. I cant remember ever seeing anything quite like that in any other city that I have been to.
It was not far off 40 degrees C when I was there, so too hot to travel around and too hot to cycle. The city centre has some old nice historic buildings, and as mentioned above the modern museums are very impressive indeed from the outside (we did not go in)
We spent most of the time in an airconditioned restaurant eating Paella. It was too hot to got outside for very long., so I feel like I missed a lot of what was there. So I would say don't go in the height of summer for this reason.