Dublin was underwhelming, and I lived there for a year around the millennium, I don't know if it's more whelming now.
Barcelona I love, lived there 5+ years, try to visit at least twice a year, more If I can: I chill out in Gracia, go round the Labyrinth - great view of the city, usually really quiet. CosmoCaixa to say hi to the capybara, El Born for takeaway pizza, Rambla Catalunya for people watching and to see the Flirty Giraffe.
Tunisia left a really bad taste, but it was 1993 and I was 17. Again, things may be less awful now.
I love Pyrenean France/Languedoc-Rousillon (scuse spelling?). Saw Carcassonne on a windy Easter day - pretty much had the place to ourselves. A friend raved about Narbonne, but while pretty, I was expecting amazing, so felt a bit meh.
San Francisco we loved in 2010, didn't feel dangerous - until we got lost in the Tenderloin district looking for a cinema! I'd love to go back, but having seen the news, most definitely no.
Venice I adored. Went in 2005 for a special birthday, super-cheap ryanair flight, 3 nights in a 3* in Mestre, over the bridge. We travelled in every day by bus with mostly Venetians, very few tourists. It was the end of April, so not full of kids off school, not heaving with people, not too hot, no smell whatsoever. We walked, and walked, and walked, found tiny cafes, authentic food, cute bars full of locals, saw a wedding - B&G climbing into a gondola outside the church. Honestly, it was a magical 4 days.