During the peak season, the town of Samarkand puts on this horrid light show. I find it disrespectful to the buildings and everyone involved with them. (It has to be pretty bad if I find it disrespectful). The buildings themselves are beautiful though.
Visiting the Registan during the day is far better than visiting it at night! Just remember to try to haggle on the ticket in, they usually knock off 30-40% right off the bat.