I have been playing a bunch more Civilization 6, and while the addiction is strong there are some fairly serious frustrations I have with the game. One of the things that the theme of the game supports is the idea that wonders of the world are really important and powerful. They are unique in that only one copy of each can be built, they often have tricky placement rules and requirements, and they all have cinematics and quotes associated with them. Finishing a wonder is obviously supposed to be a big deal.
It usually isn't. In fact much of the time finishing a wonder is mostly just a good time to mourn all of the production you poured into making it, and wonder why you didn't spend that production on something useful.
There are certain kinds of bad wonders that I have no problem with. For example, I don't think that Stonehenge is a good wonder. It is useful if you want a religion because it gives you one right away, but if you go for Stonehenge and someone else beats you to it your early game position is awful because you threw away all that production on something that isn't new cities, infrastructure, or military. It isn't good for a religious game particularly because if you are doing that you want to build holy sites and shrines and such anyway. I don't think there is a strategy in which Stonehenge is the best build.
Big Ben is another crazy wonder that doubles your current treasury. If you are in the late game and the other players let you stockpile 10,000 gold and double it then sure, Big Ben is ludicrous. So what though? If you have done that you have already won the game anyhow. In any game where you pull off a massive Big Ben you are just winning more.
Both of these wonders have unique effects, but I doubt they are ever actually relevant or a good idea in terms of optimal play. This is fine! The wonders I have a problem with are the ones with boring effects that are also bad. There are wonders that are basically comparable to generic buildings, but they suffer from the possibility of getting blown out if someone else finishes them, they occupy a space on the map, and they have restrictions on placement. Plus they take a really long time to make so they come online slower and make timing other builds more annoying.
A wonder is a risk, and comes with real costs, so it should be exciting. You can make something exciting by doing something unique, like Stonehenge or Big Ben, or you can make something exciting by making it powerful. But if you make a wonder like The Hermitage, you have a wonder that is barely better than a regular building and costs an enormous amount of production, in addition to the basic risks of placing a wonder. It is an embarassment.
I don't want wonders that are as powerful as wonders were in Civ 1 and Civ 2. Those were world shattering in many cases, easily meaning the difference between a sweeping victory or crushing defeat on their own.
One serious struggle in terms of wonder design is long vs. short term. The game really shouldn't go beyond turn 250, and a lot of late game wonders can't possibly pay for themselves in less than 50-100 turns. They literally can never be worth the production you pour into them before the game is over. Some wonders, like Big Ben or Oxford University, immediately give you their benefits so they are surely worth building. Others, like Forbidden City or Colossus have slow benefits and those are going to rarely pay off sufficiently.
All of this is mostly sad because when I look at a city build queue I should be excited by my options. I should wonder if I ought to take the risk of building Forbidden City for that huge payoff when it arrives. Instead I pretty much just ignore the wonder section because there isn't any point. I would be far better off just building normal buildings, infrastructure, or troops. The real kicker is that even if there was no risk of someone else building it out from under me I wouldn't want to build most of the wonders anyway! Risk should come with reward, and the way the game is now most of the risk comes with no reward at all.
All this makes me want to get back into modding. I spent a year tinkering with Civ 5 and I absolutely loved doing it. One of the most critical things I was doing there was making sure that each wonder, building, or troop had a place. They don't all have to be good in every game, nor even part of optimal lines of play at the highest difficulties. They just have to have some way to shine, some reason to be there. You don't have to say that Forbidden City is the thing to rush for, but you should at least be able to say that when you finish it you look at what it does and are excited that you snagged it.