I thought it started going downhill with season 4. The writing and comedy got too childish and lazy. When Jessica was in the hospital, seeing the 4 men fight over her was funny the fist time, maybe a little the second time, but they kept that going on and on and on almost forever and it became disgusting to watch.

He was definitely missed, but the show had so many other great characters to keep it going. Roscoe Lee Browne was OK, but he was no Benson. The first 3 seasons were excellent, the 4th was not as good, but still better than most sitcoms.
Robert Guillaume left so he would have a lead role in his own sitcom,but he did not have the strong supporting actors he could play off of as he did here.