Yes, cities are (almost by definition) more crowded. What is subjective is when they become overcrowded. By a pragmatic metric (say, infrastructure spending per capita) that's not happening in cities even most Europeans would consider overcrowded.
They're also louder, but that noise is contained within relatively small pockets. Fans of quiet suburbia need not worry.
Every big city I’ve been too has been dirtier than low density suburban areas of equivalent wealth.
Cities are definitely louder than suburban streets, if they’re in cul de sacs and not next to a main throughway.