Two words, Iberico ham.
That may be all anyone needs to put Barcelona on their top of anything list. If you've never had it or don't know what it is, there really isn't a way to properly describe the experience of the ham actually melting in your mouth.
I had been to Spain a few times prior to my first visit to Barcelona. This (above) is early February of 2013, wedged between trips to Ukraine, Vietnam, and a looming deployment to Afghanistan only a few weeks away. I was trying to make the most of life and Barcelona was definitely a good choice for this.
February might be a little nippy for a swim in the sea, but the beach was ample and the sunshine was good. The seafood wasn't the city's strong suit, I don't think. At least I had tracked down a place for razor clams and they weren't at all inspiring, rather gritty garlic tubes.
However, as mentioned, the hams are worth the trip alone - the places in which you can enjoy the hams and the other accompanying tapas treats really left a long lasting impression on me. Barcelona might be my pick over Rome or Paris or many of the other classic destinations of Europe.
La Rambla is maybe so popular it's a cliche, but I couldn't have cared less. It's a nice place to people watch while pinballing vendors and architecture.
Barcelona's parks are definitely a strong suit, while I sometimes enjoy a theme to explore while discovering a new destination. Barcelona's Gaudi repertoire does not dissapoint.