The in my eyes worst designed civs:
America:
I really dont know what to do with America. Its a cool feature to steal land of neighbors, but you will always rise tensions with your neighbors as a downside. Gaining yields by purchasing tiles also such a mediocre thing, good on paper but the yields are only coming to you if you really have the money to permanently buy tiles, which normally dont happen. While the landgrab of the US may be historical correct, but it isnt a really interesting game feature. The whole thing feels a bit uninspired.
Ottomans:
Its nearly the same as Portugal, a wider range of yields are possible. But instead you are always in fear of getting nothing cause your trade partner declare war on you or your unit gets pillaged. There is also permanently the pressure to chose short range trade routes to trigger your UA more often but have to pay that with less yields by the trade route itself. Their unit is awesome, no question, but on the other side, their UB is so meaningless, that I really dont care about it. I agree with others, that you have with their UA on the one side an ability, which forces you to hold peace, while having on the other side 2 abilities, which pushes you towards war. That UA should be really changed, cause its in my eyes only a worse version of the Portugal UA and doesnt have any synergy with their other abilities.
Germany:
I am a German. I really like to play Germany. But it isnt a good concept.
What carries Germany the most is the Hanse building. 10% of the gold is added as science and 50+% production bonus is simply a ridicoulus strong bonus.
But you have to play Germany always the same. Pick statecraft and send all your trade routes to CS. And this means very often never using any internal trade route and also using trade routes to CS and only gain +4 gold from them, while other options with +10gold +6 science +4 culture etc are possible. I often play the huns peacefully and even they have war aspects in their UA, I dont see it as a loss in not using them. But beeing forced to pick horsehockey trade routes only to activate my other abilites feels simply odd. And +1 Delegate per 3 allied city states is nothing. If you have to face a human played Austria in game as Germany, you are gone. You are simply gone. Their whole build up is a win-more construct. But doesnt really help in coming to the area, you are winning.
The Panzer is in my eyes ok. I play very often early and mid game peacefully and activly wage war only in the late game, so I dont see that much problem. I think using Landknecht as their UU would fit very well, the name itself is already german, and would push the bloom of Germany more into earlier stages.