I recently marathoned most of his films and boy is it just a fascinating, winding run of work. He was untouchable from his early days all the way up to The Apartment and One, Two, Three but then it was a slow and mild decline where the times were changing faster than Billy could keep up. You go from the taboo of Jack Lemmon renting his apartment to adulterers to him nearly appearing full frontal in Avanti! 12 years later. It got staler and staler and finally, with Buddy Buddy, his filmography was officially declared deceased. Still the 40s and 50s run is undeniable with some all time greats and he's likely a top 30 or top 25 all time director in my eyes.