@sellotape12 I have exactly the same experience, every other person I know seems to love the place and I just don't get it, it's like we went to different cities! (Funnily enough we were in Berlin at Easter and it was bloody brilliant, absolutely loved it, would happily move there!).
We stayed in an Airbnb on the edge of the Bairro Alto with the sweetest owners, they were so lovely and friendly. But out and about I just found it, grotty, sweaty and a bit tense? DH and I both said it was like Shoreditch back before it became cool, OK for a night out but a bit grim for a longer holiday. The cobbled streets were really slippy, felt like I was always 2 mins from a broken ankle, the mess/rubbish was literally everywhere, it was very hot but there didn't seem to be any space to just breathe and watch the world? Everything was too narrow and pokey and there was too much traffic. The castle was crap - I mean, European landmarks are never that interactive or engaging (high five to the National Trust) but that one was particularly desolate. We got hassled by loads of street sellers, we travel a lot and I haven't felt so on edge about pickpockets since we were in Nairobi years ago.
We liked the aquarium and the water gardens. Belem was OK, ish. Bit empty and souless.
I guess we are quite active holidayers, and maybe if we went for a weekend of just bars, nightlife, mooching and cocktails etc we'd feel differently? My friends think it's amusing how much I hate the place.
We went on to spend time on the coast and a week on the Algarve and loved both of those.
And fwiw I feel the same about Bilbao. Hated it and the people were miserable so if that's on your list maybe cross it off too 🤣