I spent five days there in May. I fukking loved it. The top spot everybody will tell you is The Sagrada Familia. If you love seeing monuments and classical buildings it is worth peeping. The greatest building I've seen in person. Just the level of detail on the inside and outside. It was amazing. We saw a flamenco show which I didn't expect to like but by the end loved it. Just walking around the city and just at every turn beautiful buildings. The women were gorgeous and so much walking happens that so many had sick bodies. Plenty of great food to eat. Only thing I didn't experience was the nightlife or hitting the beaches.
If there for multiple days I'd do the hop on hop off bus for sure.
Barcelona is my favorite city. Love the culture, architecture, vibe of the city. Love the city element of it, but you're within minutes to amazing beaches. Plenty of beautiful women, with good food, and fun neighborhoods to explore. Couldn't tell you anything about the nightlife and clubs, but from what I can gather they have it.