Let me start off by saying I have no nostalgia for this game, I didn't grow up with a PS3 and the very first time I played it was back in 2017 so this is only my 2nd time playing the game so when I say it is my favorite in the series it is through a fresh experience and not rose-tinted glasses.
God of War III features bigger and more grandiose set-pieces and locations, the sheer scale of the game is just insane exploring everywhere from Hades to the heights of Mt Olympus and who could forget the breathtaking, awestriking view as you climb the Chain of Balance or move the Labyrinth cubes in the cavern. I still think God of War I&II have more of an adventurous feeling since in God of War III you're mostly just in Olympus the whole game, but the sheer scope and scale of the locations and set-pieces more than make up for that.
Of course the locations are not the only thing that is bigger and better. No, the boss fights are easily some of the coolest and most epic in not only the whole series, but action video games in general. God of War III is a game that revels in its gory spectacle and every boss fight is just a joy to watch unfold from the very beginning of fighting Poseidon on the back of the Titan Gaia to carving off pieces of Hades flesh or ripping off fingernails from the Titan Chronos as you scale his body and even getting into a bloody fist fight with Hercules (Shout out to the devs for getting Kevin Sorbo who voiced Hercules in the iconic 90s show 'Hercules the Legendary Journeys' to voice him in this game as well). God of War II introduced epic boss fights with heroes and demi-gods from Greek myths, but in God of War III you actually get to fight the gods themselves and I was never once disappointed with how those fights played out.
Combat is mostly the same as the first two games, Kratos still has his primary blades (Known as the Blades of Exile in this game) alongside various magic powers and other weapons you pick up on your journey like the Claws of Hades or the Neman Cestus. There is one major addition to the formula like the Item Power bar which recovers over time after using secondary items like Apollo's Bow or Herme's Boots which are mostly used for platforming and puzzles, but also have combos tied to them which can add an edge in combat. This is the most polished, fast, fluid and complex the combat formula has ever been in God of War to date.
The story for God of War III is once again a tale of vengeance as Kratos butchers all the greek gods one by one on his path to Zeus and causes an apocalyptic event to befall the people of Greece. This time Kratos must quell the deadly Flame of Olympus to once again use Pandora's Box against Zeus as he did all those years ago against Ares and to do that he must find Pandora herself. God of War III expands the world and lore of the series in clever ways that often even tie back into the very first game flipping what we thought we knew on its head and I love that. Also I will say how I saw that at the time of this game's first release a lot of people complained about the ending and found it weird, but I love the dynamic between Kratos and Pandora and how she helps him develop and grow and it fits even better after playing God of War (2018). So I would say that God of War III ended the trilogy in a very satisfying way because while it is very dark and tragic there's still a glimmer of hope for the future as well.
God of War is a series that has only gotten better every new entry (At least in terms of the original trilogy) God of War (2005) set the standard for action/adventure games, God of War II redefined that standard and raised the bar in every way imaginable and finally God of War III mastered and perfected the formula. Featuring more grandiose set-pieces, some of the most epic bosses in the action game genre, the best God of War combat system to date and a well written story that gives a satisfying conclusion to Kratos' vengeance filled trilogy, God of War III is everything I loved about the first two games, but turned up to 11 making it the definitive God of War experience.