I thought the story arc was complete in GF2. Michael has won the whole world but lost his soul. He's murdered his own brother and irretrievably alienated his wife and stepbrother. I didn't think the story had anywhere to go from there. So even if GF III had been a better movie, it still would have been unnecessary IMO.

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.