The japanese GTA thing used to be said about the games back during the PS2 days and it's a horrible description.
They have a very condensed world, like 20 city blocks that is stupidly detailed and full of side activities. So it acts more like a hub than a sandbox. It's usually Kamurocho and another city/town, with Kamurcho being the same skeleton with iterations since Yakuza 1. By Yakuza 0, it's so jam packed with s*** to do I've spent about 160 hours on it and I'm still missing stuff. Side activities are broken down to absurd and well localised sidequests, several minigames of varying depth (from bowling , fully emulated Sega games like Outrun and Virtua Fighter and in depth building/racing toy cars on which I've spent an embarassing amount of time), consumable/weapon/sidequest related shops, roaming goon encounters and boss fights and restaurants/bars with food/drinks that give exp and bonuses. There's usually a big side story like running a cabaret or RTS gang management, depending on the game.
I actually don't have much experience with 3D beat-em ups (there aren't many of them anyways) but it's probably the best one I've played bar Godhand. It's miles ahead of western attempts like the Batman games. Yakuza 0 in particular has so many moves, both offensive and defensive, that it never got stale. A big part is due to the feedback of the hits and heat moves which are contextual actions that change depending on the state of the enemy, whether you are armed or not and with what weapon, the location of the fight etc. The enemy AI, bar bosses, ain't anything special though.
The main story is both stupid and hype. Usually driven by character conflicts but it also doesn't give much of a f*** about consistency if it wants to set up a bossfight. It's pretty much testosterone the game, without taking itself too seriously. The cutscene direction is the best in the industry and I regularly spam the discord with Yakuza music.
That's pretty much all Yakuza games with Yakuza 0 being the one that executes it best. It also has 2 very distinct characters to play as and the best iteration of Kamurcho and Sotenbori. Fully worth the money and my 2nd or 3rd favourite game this gen. I have a revew up on Kiwami's GameFAQs page if you wanna see my view on why that's not as good. But if you like the main formula, you'll like all of them unless you get burned out quickly.