As for the civs:
God tier: China, Scythia, Brazil
Potential God tier: Germany, Aztecs
Awesome tier: Spain, Japan, England, Egypt
Good enough tier: America, France
I think so far with the exception of England they're all pretty well balanced. For example:
- Egypt gets a bonus at ALL periods of the game to wonders. Unlike china who is only early or france who is mid. Also their chariot archers are FASTER, STRONGER and RANGED and they're available almost at the start. They are incredibly powerful and deceptive. I think you'll find then near Aztec/Scythia tier in early military (unless it gets nerfed). They also get the sphynx for early culture and faith and their trade routes are both better and more attractive to others.
Imagine Egypt as a Scythia that gives up some of it's military for a LOT of other bonuses.
- Japan:
It's been shown that japan also gets 1/2 price campuse(science), holy site(faith) and culture districts. So they will be building a lot of districts.
Now consider that when they place districts next to eachother, it's like the brazillian rainforrest. So when they get 3-4 districts next to eachother (note: it seems that districts from other cities count so you can place 2 cities close and put their districts adjecent to eachother) it's like having rainforrests next to ever one of their districts.
Sure Brazil will start stronger, but Japan will catch up quickly, with more campuses and then get ahead. More importantly: Japan doesn't only get that bonus on cities next to rainforrest. It will get this bonus in all cities.
- Spain
(it's actually the civ's that has made people most excited) nuff said. Although consider that unlike other civs that get bonus combat ONLY on their continent, or only for 1 unit in the game, spain gets +combat to ALL units in ALL era's against people not following your religion.
Mixed with their entire range of other bonuses, ranging from unique buildings to unique units that also act as a unique ability and bonus to trade and naval, I think they're god tier.
- America
I think they're very much udervalued:
The bonus home continent combat means that a scout can fight par with a barbarian warrior (if you have the +5combat policy). And your actual military will destroy enemy barbs.
You can use that to expand quicker.
From there you can capture the person who starts on your home continent (I think Ed Beach said its 2 civs per continent roughtly), or you can defend yourself against countries like Scythia whose bonus will only last a short time.
Then there is the legacy bonus: we know that the gov. bonuses are huge, you have +15% wonder production which is pretty much egypt/china/france but for all eras, you have +4 combat bonus similar to having a unique unit on every unit.
So imagine keeping twice as much of that bonus than anyone else. It's both powerful and flexible. One game you can be China, the next you can be the Aztecs etc...