Nah Detroit has some beautiful architecture and really surprised me when I visited last year. Also being on a river and next to a lake is a nice feature. I've been to plenty of more depressing places in the US
Mostly any ex-steel based industry town in the rust belt except Detroit, only because it has been the focus of overt development to directly impact its image as a wasteland. Not sure what took its place.
In Bucharest in the last years the mayors fought back quite successfully against those all-covering billboards. However enjoy it while it lasts - we just had local elections and the old mafia got back in office, so I bet the billboards will be back very soon (and cables hanging off every pole and expensive concrete wastelands and and and).
Really? I thought the old area along the west bank of the Vistula was nice. I didn't see much of the rest of the city, but most cities are uninspiring outside of their central areas.