It’s a fantastic city, one of my personal favorites (I’d rank it up there somewhere with Rome, London, and Paris, possibly above them–depending on mood). Great food, great art, great people. In my limited experience, I found Barcelonians generally friendlier than people in Madrid or Andalusia (the only other parts of Spain I’ve visited).
This difference may be due in part to the Catalan character of the town and region. You will notice Catalonian flags and signs in Catalan (usually bilingual, IIRC) around Barcelona, though everyone can speak Spanish. I can’t speak to exactly how sensitive the locals are, but it’s clear that many of them take immense pride in being Catalan first and foremost. As a foreigner, I doubt you’d be expected to be completely versed in the regional politics, but I’m sure that some awareness of the cultural distinctions will be appreciated.
The downtown area (the old city) is charming, and includes the real medieval cathedral and the harbor. The Picasso museum is also in this area (and includes several of his earlier paintings, done before he moved to Paris–some of his best stuff, IMHO). Parts of the old city, and Las Ramblas (which connects the old town with the newer parts to the north), can be a bit sketchy with pickpockets, as already mentioned–but it didn’t strike me as particularly dangerous, and seemed comparable to other major European cities.
The Eixample neighborhood, in the newer part of the town, is more upscale, and has an almost Parisian sensibility with wide open boulevards and designer shops–but a lot less expensive than Paris. A few of the Gaudi houses are in that neighborhood, and I’d highly recommend at least walking by them–the Casa Mila and the Casa Batllo in particular.
If you like Gaudi, I’d second (or third, or fourth…) visits to the Sagrada Familia (technically, not a cathedral but an expiatory temple–not that it will make much difference) and the Parc Guell. They’re a bit more isolated from the other sites in town, but worth the extra journey. As beautiful as they are, they also make you wonder what they would have looked like if Gaudi had ever finished them (though we will one day get to see the finished Sagrada Familia, hopefully–they’re still working on it, 83 years after Gaudi’s death).
THIS sounds like a story! Or is this just common wisdom? Do tell more.