Hong Kong. Depressing, grey, like one giant 80s shopping precinct. Nothing much to do or see. Not even good shopping. Really didn't like it, apart from a day when we got the ferry to an island with a huge Buddha statue you clamber up a billion steps to get to, which was much nicer.
Oslo. I thought it was an armpit. Everything was closed on a summer Sunday. Offensively expensive. Again, oddly enough, the nice bit was getting a ferry to an island and then a tiny boat to a tiny island (was there for a wedding on said tiny island). Beautiful and quite Tove Jansson's The Summer Book but with a massive BBQ and singing and dancing 
Sydney was underwhelming for me too: a smallish and quite provincial place that's somehow convinced the world it's a glitzy and buzzing international metropolis. I liked Melbourne a lot though; characterful and handsome, lively culture, friendly people.
Liverpool was great; went for a day to visit the Tate, which was fab, but found so much else to do as well. Loved walking by the water.
Unlike a lot of people, I don't find Paris grubby and I've always (four visits) found the people usually friendly and helpful, at worst polite. Have found myself in lots of charming areas, shops and cafes purely by chance.
Madrid. Didn't expect to dislike it per se, but was pleasantly surprised by how warm people were and what an easy city it was to spend time in –a nice caff or restaurant round every corner, amazing flea and antique markets, lots of galleries and museums. Loads to do and very accessible all in all.