Crowded is a relative term - its all in what you are used to. IMHO there are few uncrowded times anymore. Between the parties, the festivals, conferences, sporting groups, etc... That said, some times are better than others.
I still long for the empty days of 1998 and e-nights so any level of crowd is a crowd to me! We also go every May and have found the levels of guest increase each year, but if you go early, use late entry you can beat some heat some late starters.
Boy I miss e-nights!