By the way, a few comments from me.
I started with Prince and played King too (what I played in Civ5) and I think the difficulty is rather close. However, city states are sooo good because you can get more delegates. And when you get more delegates, you can pick yourself as host. When you do that, you get more delegates. Then... You get the idea
Once you get strong in congress, it feels noone can stop you.
I like the whole tourism thing though, it added some depth to tourism and more reason to have culture even when you don't go for a culture victory, not to mention more depth to picking how you spend your culture. I'm sure the community will find the best ways for higher difficulties, but still, there is choice.
I also like the diplomatic option increase due to world religion-world ideology thing and the diplomatic relations due to ideology.
Trade routes are again a good addition, especially the ability to send food-production to your cities (also, new quests for CSs, yey).
Only thing I kept thinking negative is the amount of choice in Congress. I mean, there are many options but you run out of some of them fast, especially if nations meet early and you don't want hostility.
That being said, I'm definitely no Civ expert. As I said, I play King. (I guess I can go one step up) I'll translate my preview if I can.
PS: I cant recall if it's in screenshots, I noticed this later. Merchant of Venice also has an ability whose explanation reads "double trade mission bonus", if memory serves. I'm not sure if it exists in Great merchants (maybe triggered in certain conditions) or a constant thing.