The most striking place you can notice this is at Niagara Falls in NY. The US side is dirty and tired. Walk across the footbridge to the Canadian side and its like walking into a sci-fi utopia of cleanliness.
Although, being a US citizen, I'll say that what I notice most when visiting Europe is that the graffiti seems 100x worse to my eyes in most European cities than in US cities. Italy seemed especially bad to me. It's like some child has drawn on the walls of Europe with crayons.
Another interesting point to me is Sydney, Australia. I had visited it as a child in the 80's and remembered a very grubby, dirty city. I visited again a couple years ago and found a beautiful, clean, enjoyable city.