Though the original posting was clearly trolling (calling a Civ "worthless"
), this thread at least has spawned several thoughtful replies. Japan has been hurt by changes in gameplay and are currently underpowered, but they are not "worthless" and these forums have whole articles on how to play Japan well.
adwcta made an amazing post earlier that I wholeheartedly agree with and encourage everyone to read. In addition to his post, I have some quick thoughts:
*Bushido: Japan's UA clearly has been hurt by the changes post-G&K. Not only has the negative modifier for damaged units (which Bushido negates) was changed from a -50% maximum to -33%, but the change to the 100hp system means units spend less time in the red (in other words, units need Bushido less often). The developers have very recently said that they're taking a look at Japan because the UA is less effective now, and, worse yet, Bushido is a passive ability that doesn't effect how the player plays. If Japan's UA is changed, the developers have said they are looking to make it more active (i.e.,
not the passive "obvious" choice that people keep citing to of being more resistant to tourism - that will not change a player's gameplay the way the developers want).
*Samurai are an amazing unit. Let's get this out of the way:
Samurai do not obsolete with Gunpowder. They obsolete with Metallurgy. Musketmen, which are only slightly stronger in base strength than Samurai,
co-exist with Samurai. And Samurai upgrade into Musketmen at a pittance. A Samurai can be popped from a city with the Siege promotion, Great Generals 2 (which does produce a TON of Great Generals over the course of a game - great for snatching strategic resources), and then can instantly be upgraded into a Musketman to get your Iron back for your next Samurai. Rinse, repeat, and enjoy your swarm of Samurai Musketmen (or Riflemen, or Great War Infantry...) for the rest of the game.
*The Zero: Does suffer from the fact that it's a late game unit. And a unit that doesn't see much play because 1) it's situational; 2) fighters aren't a very good value compared to bombers; and 3) the AI traditionally hasn't managed its air force well. That last part is indeed changing in BNW. As a defensive unit, the Zero does an amazing job, but because it's largely never seen and not needed, to most players it will be lackluster.
Japan deserves some scrutiny with the changes in game play Civ5 has seen, certainly. The Samurai really carries Japan, in combination with Bushido. But that combination is still powerful in the hands of a competent player.
Japan needs a major cost reduction to military. It is in their lore. People didn't fight for money. They fought for honor. Lives were dedicated entirely to the daimyos. This should be reflected with 25% unit upkeep. So they spend 75% less to upkeep their armies.
Historically, this statement is on very shaky ground. Samurai during the warring states era (Oda Nobunaga's era) were mercenaries or fought for their livelihood by supporting their feudal lord. Honor had very little to do with the Samurai (in fast they're the villians of a lot of historical tales) until they came to be romanticized after Cmdr. Perry broke Japan open to foreign trade.
Not to mention your proposal is like Germany (who are more often mention for a overhaul than Japan), the Zulu, and the Ottomans.
And we've got enough faith civ's, really. The focus on warfare is certainly appropriate for Japan. I haven't played it recently, but the UA was originally considered to be extremely powerful, so they must have nerfed it or something.
The samurai itself is fine, it's the mayfly-like lifespan that longswordsmen have before musketmen appear that's the problem. They need to rework the tech tree so that there's more of a gap.
As I and other posters pointed out, Bushido was indirectly nerfed by changes in gameplay mechanics.
And as I describe above, the short time between Longswords and Muskets is actually a boon the Samurai, not a hinderance. You actually have all the way until Metallurgy to keep producing swarms of Samurai that can be quickly upgraded to Rifles.
Their isolationist tendencies could be interesting for a UA. Give them a resistance to other civ's tourism (related to open/closed borders perhaps?). Maybe even grant them immunity to ideological unhappiness?
The Devs have said they're looking to make Japan's UA more active and less passive. Your proposal would make Japan an annoying AI, but not more fun to play.
Yes they are terrible. What is so special that they start with Shock I promo. Seriously they are very underpowered. They could have made them a really badass UU & a game changer instead of bland bonuses.
First off, Samurai have Great Generals 2 in addition to the free Shock 1 promotion. Secondly, the free Shock 1 means a new Samurai born in a city with a Barracks and Armory gets a free Siege promotion. A few Samurai will absolutely savage a city on open terrain. It's amazing how quickly they fell a city like that.
The UUs aren't fantastic, sure, but the UA is more-or-less priceless when it comes to taking cities, especially in the early game.
This is certainly true. If you're having a tough time taking a city, Bushido does help you power on through. Even now in BNW.
Well, I still highly doubt Samurai are that good on Prince, but I only played Prince once and it was Persia with it's crazy move bonus, so the game was decided long before Longswordsmen.
I consistently find Samurai to be good on Emperor. I'd imagine you'll find players who can tout their usefulness on Immortal and Diety. They could seem underwhelming to a player who's not paying attention, but there's a reason most of the Japan War Academy article focuses on them: they are deceptively AMAZING.
I won't dare to say it is the worst unit, but it is nothing to be very excited about.
They are so overpowered, here I thought caroleans were the most beast units 'til later eras 
