It is trying to die faster than "Like a Dragon: Ishin!".

The story is pretty good, it serves as a good insight on what happened before the events of "Yakuza: Like a Dragon", it also spoils the events of that game so if you planned on playing it after "Yakuza 6: The Song of Life", you'll have to keep that mind.
The characters are far from unique, as they just make the same characters every game (1 prettyboy killer, 1 brute, 1 that helps the main character, and of course the mastermind/s), but the villains were still well written compared to some previous games, because you can actually understand their goals and maybe even agree with them.
Despite only 5 chapters, the length of the game is pretty decent, there are plenty of filler missions to stretch it out but I didn't complain, as I wanted to experience it as much as possible.

Side content is also solid (not the hostess dating), the new Coliseum is awesome (to some degree), and you can even dress up Kiryu for the first time, as well as play as more than 30 characters in the Coliseum. Now, those characters' movesets are obviously extremely limited, but it is a step in the right direction and I am looking forward to seeing more of that in their future beat 'em ups.

As a hardcore Yakuza fan, it hurts me to write a negative review but making a positive one would be overlooking all the major flaws the combat system has.

1. The combat's main combo mechanic is air juggling, but there are only 7 launchers? If we compare it to Lost Judgment (which is what this game wanted to copy but did a horrible job of), that game has so many launchers people can't even count them all.
Now, those 7 would mean something, had there been JUST 1 that works consistently, and the 1 that had potential to work consistently (wire pull), does NOT work on any stronger enemy such as bosses and mini bosses, as Kiryu is apparently not strong enough to pull a 140lb femboy with painted nails.
Five out of seven launchers require you to do an extremely slow combo beforehand, during which you'll get hit a billion times and then the enemy will most likely dodge or block the launching move. Now you're down to only 1 launcher to rely on for stronger enemies (Agent EX Light X2). Sure, there are ways to relaunch enemies with this one to make the combat a bit more fluid. But is 1 somewhat consistent launcher what you want to see in a combat system that focuses on air juggling?
Cause you sure as hell can't do ground combos to mini-bosses or bosses without getting countered.
The fun dies faster than an unvaccinated baby.

2. So you finally launched an enemy? Great job, now what? Did you expect to juggle the enemy for at least 10 seconds? Poor you. The developers have coded a specific 6 second limit after you land your first hit, after which the enemy is simply going to tank your hits and drop to the floor. Why? They removed Lost Judgment's damage reduction so they thought, juggling for too long would be too OP, there shall not be a juggle longer than 6 seconds. You expected a moveset with a decently fast combo speed to land as many hits as possible in that short time period? Too bad, cause you're not getting it. The original (Yakuza) style's combo speed is slower than Saejima's in Yakuza 4, it is so slow it will remind you of Yakuza 0's Mr. Shakedown.
What's even sadder is that the developers coded a combo speed boost on the Yakuza style, and it activates when THE ENEMY IS LYING ON THE GROUND. Thanks Sega. I simply couldn't wait to execute some amazing combos on a helpless enemy collecting dust on the floor.
The "Agent" style's combo speed is not great either, it's similar to the Yakuza 6 non-upgraded combo speed, but its rush combo has probably twice the amount of hits so it's unnoticeable.

3. Okay, the Yakuza style is bad. The Agent style can't be THAT bad right?
Well, you know how weak your punches are in your dreams? No matter how hard you swing, you can't hurt anyone? That's essentially Agent style.
Its combos work well only on weaker enemies, because if you try to bluntly attack any stronger enemy with it, you'll be shut down very quickly. The gadgets are cool (wire and cigarette especially), and extremely overpowered when upgraded fully, but just like the combos, you only feel their usefulness when you are fighting weaker enemies.
With the wire you can pull a dozen enemies and throw them as you wish, and the cigarette can blow up a whole group with ease.
On stronger enemies, the wire doesn't work, the drones are just poking them uselessly, unless you fully upgrade them, then they still poke them but deal more damage, the serpent has 1 use and not what the developers intended, and the cigarette is just.. the cigarette.
It also has no skillful counter attacks, only 1 braindead dodge counter that you can spam as long as you're in EX-heat, if just 1 of them served as a launcher I probably wouldn't even be writing this review. Actually, I still would.

4. Certain moves that were launchers in Judgment and Lost Judgment are no longer launchers for absolutely no reason (for example Yakuza style reverse Square X2, Triangle X1), and certain moves that were very useful in Yakuza 6/Yakuza Kiwami 2 were also removed for, again, absolutely no reason.
You cannot grab enemies from behind anymore, which automatically removed about 4-5 very useful heat actions.
The Yakuza style grab & throw is now a reuse from Yakuza 0's Brawler style, instead of bringing back the spin which was extremely useful in group fights OR God forbid, making a new throw.
Finishing holds which were the primary crowd control tool, now require you to be in extreme heat for, yet again, absolutely no reason.
Timing for the infamous "Komaki Tiger Drop" has also been shortened, as if Kiryu hasn't been using it for over 15 years now, making it an inconsistent tool to get rid of enemies with a lot of health for, you guessed it, no reason whatsoever.
Remember the parry from Yakuza 6/Kiwami 2? Removed.
Remember how you would grab enemies in the middle of their attack to shut them down? Removed, you immediately get punished.
Remember the Lost Judgment "floating state"? That random mechanic when the enemy doesn't fall to the ground anymore as long as you keep hitting? It still exists in Gaiden, but you have a higher chance of convincing a flat earther he's wrong, than getting an enemy in the "floating state", which would be the only mechanic that could save Gaiden's combat from getting old extremely fast.
I definitely forgot a few.

5. The battle design.. Oh boy. Nearly every fight after the first chapter has a couple of enemies with guns, that will shoot you through their allies, so before you do anything, you have to go around the map and take out the gun-wielding enemies one by one. Does that sound fun?
On top of that, almost every long battle has you facing multiple bosses/mini-bosses at the same time, which the game absolutely DOES NOT prepare you for. Don't believe me? Just take a look at any YouTube video recording that type of situation. What you will see is heat action spamming to get rid of 1 miniboss first so they can at least have fun with the other (and even that's rare, most people just cheese both). Does that scream quality combat system? You know how in "Sifu" you can handle multiple stronger enemies at the same time in style if you're skillful enough, by utilizing punching, dodging and parrying? Yakuza developers have not heard of that.
I should also mention that the enemy AI, which was perfect in "Lost Judgment", was also changed and now multiple enemies attack at the same time, which wouldn't be an issue, like it's not an issue in "Sifu", if you could manage multiple enemies stylishly, instead of spamming the wire or cigarette bombs, or if you want to get hit, you can always just mash your controller and brute-force your way through.
My 9 year old brother will definitely enjoy that!

I'd say more but the review has a limit, video coming instead.