First, I would dare to say that they NAILED the United States. Love, love this version. Only thing missing it is more focus into expansion (pioneers, the spirit of the frontier, etc) but other than that, great job so far, Firaxis!
And now, into the others:
England: They invented capitalism, so it is about damn time that they get a trade bonus, don't you think? Also, it would be good to have more focus into their apex (victorian times) and empire building skills (bonuses for going wide?)
Spain: Exploration gallore, with a very heavy dash of religion (Isabella), please. I really loved Civ 5's bonus, as it forced you to roleplay a bit, but perhaps a more consistent bonus / reward for colonizing far away lands would be in order. Also, it would be good to have some kind of bonus for tourism, considering that Spain is nowadays the second most touristic country in the world (right after France)
Germany: Vainilla Civ 5's depiction was pathetic, thanks God BNW improved it a lot. I would love to see a more "Prussian" type of germany: Industrious and economic powerhouse, with a heavy penchant for philosophy.
France: Culturemonger + uber-capital bonus. France is some of the most centralized nations of the world, so better show it. Civ 5 BNW went into a really good direction with it.
Rome: Conquerors & builders. Huge military bonuses / UUs that would allow it to take territory, and governance bonuses that would allow you to keep and develope said territory. An emphasis on the "romanization" of its conquered subjects would also be good to see it represented too!
Greece: I really didn't liked the whole CS cum conqueror focus, Greece was a bit of a mess politically talking (it was Sparta afterall who defeated Athens, not Persia). They should be centered around building up tech, culture, and building naval / commercial outposts me thinks.
Persia: Now, this a civ that should revolve around CS (satraps!) and mantaining big, albeit not entirely governable empires. A strong bonus in faith production should also be present, I think (they founded the world's first monotheistic religion afterall).
Ottomans: One of the worst represented civs in Civ 5, I really hope that they build the Ottoman civ from scratch. Big bonuses for going tall in your capital (Constantinople!) and perhaps some kind of late game nation-building could be in order too (Attaturk!).