To me Worf became a rounded character on DS9, something he never was on TNG. DS9 gave him the opportunity to truly fall in love, experience command, meet a klingon that taught him what it meant to be a klingon in the truest sense (Martok). Worf got to loosen up, have fun and for me DS9 defines his character. In Ezri he had the opportunity to open up to someone who knew him deeply and could give him good counsel. I think DS9 would have been missing something with out both of these characters.