Hmm...
Japan: Could use a Zero replacement and a buff to the UA. They could keep Bushido and add something else too (like Seabastian's suggestion) and I'd be fine. But seriously, either do a major buff to the Zero or replace it at all.
Germany: Seabastian did some great suggestions. I wish they kept the Landsknecht, though, they're so cheap!
Ottomans: You know, I actually like the way they are. Quite versatile for land-sea combat. I don't care much for the randomness in the Prize Ships promotion, because paying only 33% of the usual maintenance costs for ships is very nice. Sipahis are also quite good, IMO, they might be a Lancer, but +1 movement, +2?1? sight and free pillaging makes it up for them. I completely changed my opinion on Lancers after the W. Hussars.
Denmark: Fine for me.
Russia: Also like them a lot! The +1 production on strats is awesome for building stuff quickly. They already got a buff with Iron at Bronze working: now they get +1 production faster and might sell the excess earlier. If you've got some friends, early game Russia might sell their ridiculous amounts of Horses and Iron for some settler buying. I agree that the Krepost could perhaps use a small buff, but it is also nice, as it makes buying those recently discovered strats cheaper. Double Uranium is awesome for obvious reasons. Also, remind that the +1 production affects all the strats, not only the doubled trio of Iron-Horses-Uranium, so, even if it is late gamey, Aluminium, Oil and Coal also get +1 production. It is best early game, though, when St. Petersburg has to build a quick library... And the Cossacks are one of my favourite UUs! +33% vs. wounded is not the same promo as Charge, so you could get a Cossack with up to +100% vs. wounded units! Also synergyzed by the doubled Horses and the Krepost being a barracks replacement. Russia's cool
America: Yeah... +1 sight is nice, but the tile discount? Cof cof Shoshones... yeah, Manifest Destiny is half ok half pff. Minutemen are good. B17 seems good too. They could replace the tile discount and put something more useful in the UA, I guess. There's a reason Angkor Wat is one of the most useless wonders to most people. I know it sounds weird because I just said the Krepost it good, but it could also get a small buff like +2 :strenght: for their cities or something like that. At least it isn't their UA... and Russia kind of has a reason to get that, as it gives them earlier/cheaper access to strats tiles.