It goes a little farther. The parties all take place after a religious ceremony (a wedding, a baptism, and an appointment to a Sacred Order). At the party there are always business meetings going on (Vito doling out favors; Michael and Ola and Geary; Michael Zasa and Vincent) There are also foreshadowings of things to come (Barzini acosting the photographer and Paulie lusting for COnnie's money); Ola handing Michael an orange; Vincent biting Zasa's ear). There is also photography involved where someone gets uncomfortably dragged into the picture (Kay with Michael; Geary with Michael and vice versa; and Vincent with the family).
After the set up there are also elements of the "Godfather movie formula" if I may be so presumptuous as to call it that...
After everyone is introduced the main character always has a brush with death --- Vito being hit --- The attempt on Michael's life --- Michael's diabetic stroke --- followed by a vacuum at the top which gets the family deeper into trouble with their enemies ; Sonny killing Tattaglia Jr, and Michael killing Sollozzo, and the prolonged war; The "assassination" of Pentangeli under Tom's watch; Connie, Neri and Vincent killing Zasa without Michael's permission. This is followed by the main character reasserting himself, but having to take a less aggressive posture --- Vito calling the meeting after Sonny died; Michael pretending to go along with Roth; The pope's death
which temporarily killed the Immobiliare deal, then followed by Corleone style revenge the killings at the end of all three movies. In that respect GFIII differs because it ends with Mary's death and what is perceived to be the end of Michael Corleone as we knew him.