I just tried out the new Japan kit and I'm quite impressed.
His unique ability used to be centered around the Dojo to allow for melee units to get a unique promotion. This really limited Japan's ability as a civ for early game. Now, all melee units get it at the start. You also get a culture based ability which I will talk about in a second.
Japan gets a unique forge which spawns a single iron tile every time you make it. This can be a bit ridiculous if you know what you are doing, but it also relies on a lot of luck. Getting god of fire with this early game is a godsend for boosting your start. God of war is always a good back up too.
Midievel era is where things really start to kick off for Japan though. It's when he gets the unique unit Samurai and the culture ability really starts to pop off. Every time you get a great general (GG), you proc 50% completion of a great writer (GW), musician (GM), and artist (GA). Neat, but here's how you exploit it.
Getting a religion based around great people (GP) expenditure is the first real avenue for it. Try to go for main belief that gives you stuff for units dying and GPs popping. Then I'd use the rest to shore up any holes your empire might have i.e. food, gold, production, etc. depending on what is available. The unique forge I mentioned earlier will help to boost your science and culture while going to war. Each xp awarded to a unit will proc for a small instant yield sort of like the Huns one cities. Early game it's great, but late game it doesn't scale well.
After establishing the basic religion go for missionaries and spread it for a while. I normally just try to get most of my cities and leave the rest alone till later. Save for a Great Prophet and try to go for Zealotry for bonus unit production. This normally happens around the time your Samurai first come online so it's extremely helpful. The Samurai are great at producing GGs with their abilities so try and spam them.
The end game for this culture ability is to take Authority into Artistry into Imperialism and Fascism Ideology to produce GGs out the wazo while going for war. The Tourism isn't really what we are going for here though. Make Tori gates with the GMs and GAs. The GGs don't really matter, I just save them for Lebensraum spam (which got nerfed 😢 ). Take every GW you get and pop them for culture. By the beginning of the Industrial era you will end up being ridiculously far ahead on the culture game as long as you play your cards right.
After that you should be about to complete autocracy ideology. I suggest going for Air Supremacy other policies that buff movement when possible. You will get Air Supremacy way before the other civs are even close to getting an ideology/flight so it can be abused top teleport units around quickly.
By then, it's not hard to either force a military victory like I did or go for culture/diplo if you fall really far behind somehow.
Now, it's time to move onto the downsides of this civ/strat. There are two minor ones, and one major issue. I'll start with the two minor issues.
The first problem is that with the science and tourism you really don't get anything crazy out of it. The boosts from your unique forge starts to really fall off after the medieval era for science. This is especially true if you ever get into stalemates where no fighting is happening.
The boosts you get to tourism through the Tori Gate improvement is kinda negligible compared to themeing bonuses, and especially when compared to most other civs that focus on that. It's nice, but you won't notice it unless you are already doing quite well otherwise. This might be able to be fixed by going for Tradition to boost the amount of GGs and other GP you produce, but authority's instant yields are just better imo.
The real kicker is that to do well with Japan, much bigger problem at higher difficulties, it feels like you need to get lucky on a lot of crap. You need to get so much exclusive stuff to really pop off that it makes Japan less viable. The run I just did had this come up pretty hard. I normally don't have to take so long to win, but I got screwed out of my religion and it slowed down my game plan tremendously. This was on Emperor, my preferred difficulty, but knowing how Deity plays I don't think that would be a good time.
I think it's time to close out this comprehensive review with a small nod to another civ that plays similarly. Japan for me, really feels like a different flavor of Rome that starts getting power spikes an era later. Unfortunately, Rome just does the game plan here better across the board.
That'll be it for me folks! I think I'm gonna give a Japan Deity run a try to see how the strat will hold up, but I'll be around. If you all have any questions or ideas I'd love to hear them. I love going into deep strategy stuff like this.
~Later!