For me it's not necessarily landmarks that is underwhelming, it's more the "touristy" places people seem to visit. I liked Paris for the historical buildings. Shanghai was disappointing, well it was nice but not as amazing as I had thought it would be. But the outskirts of Shanghai was amazing, I love villages and places tourists wouldn't think of going to. I like more quiet parts of countries.
Never been to Dubai and don't think I ever plan to visit there, it's overrated, all that's there is just buildings and malls, that was built on a desert.
Same with New York, I'm sure it's nice but I still find it overrated.
I love Eastern Europe though, now that's where I find beautiful buildings, been to Slovakia, Bulgaria and Serbia so far, still many places I will like to visit one day in the future.
Been to many countries, but my heart loves England, I believe British history has one of the best in the world, and the buildings and countryside we have here are amazing. London is a beautiful city too, unfortunately it's just too busy for my liking. :P