Phil Spector records have this heavy, dreamy sound that is, oddly, _exhausting_.

Your brain can't pick out the instruments being played (beyond the vocals and some of the lead instruments) so it all folds into each other. You stand there, awash in sound.

A key aspect of this sound was the monaural setup: everything was forced through one speaker and there was no stereo separation to separate the incoming instruments. Mono doesn't work very well on headphones though imo.