My own personal take & opinion:
I think that Shenmue III is a good representation of a problem many once-upon-a-time revolutionary IPs face: they are utterly unable to evolve and are now irrelevant.
When it was released, Shenmue I gave mainstream console gamers some revolutionary gameplay ideas that were either totally obscure or unheard of back then. A real day-night circle with NPCs reacting to time-of-day was all but unheard of. Shops closing for the night, NPCs going back to their homes to sleep, or stroll through the city or wake up to walk to their jobs was something that blew peoples minds and gave them an unprecedented sense of realism. As was also the fact that your character could walk inside stores and shop actual real-life items instead of weapons, armor and spells from every run-of-the-mill fantasy rpg out there. It was a truly marvelous sight to behold.
The fact that you also had to gossip and talk with people all around you to progress through the story inch by inch was also original.
But other than that, Shenmue I wasn't all that awesomesauce. Battle was problematic, characters weren't all that amazing (it's your classic 'I will avenge the death of my loved one' story, nothing to write home about), but when the world of the game is made in such a way that makes you appreciate it, you tend to invest on every little moment, and before you know it, you're a groupie.
So yeah, Shenmue was original in many ways, but at the same time - in other ways - wasn't anything special.
So what happens when the breakthrough-ish, amazingly original traits of the first game aren't original and breakthrough-ish in the sequels?
Answer: You get the 'nothing to write home about' game sequels instead. Which is exactly what Shenmue III is. It's the same archaic, problematic gameplay, without the originality of the first one.
This is a problem many pioneers face in the industry. Castlevania Symphony of the Night was the game that created the 'metroidvania' term among fans and had people screaming for games like that from the game's creator. After many years, he gives us Bloodstained, which is a good game, but created nowhere near the same noise SotN created. Why? Because it didn't evolve the core gameplay in the slightest, other than the fact that instead of spells, you absorb enemy abilities. Same shit, different day.
You can say how much Squaresoft 'ruined' FInal Fantasy with the latest entries, but the fact remains that Final Fantasy XV is a HUGE evolution over the archaic and simplified gameplay of say, Final Fantasy IV. And you can bet your butts that if Final Fantasy XV played like FFIV, no one would be talking about the series right now. Except like, fifty people.
Same thing with Mortal Kombat. MK2 is considered by most old-school gamers as the best MK ever, but MK11 shows how much the IP has evolved since then. All characters had the exact same basic moves and the only difference were the special moves. Now, all characters have different basic attacks, different combos, a cinematic story mode, various gear to equip to change appearance and some gameplay elements, and so on. It evolved the core game and is something quite different from its predecessors.
Shenmue III shows us what happens when you make the exact same game after the industry propelled forward after 20 years. Heck, even Elder Scrolls games are showing this now. These are once-upon-a-time beloved IPs that today do not produce what was that made them amazing back then.
Originality.
