I'm in agreement with the various Vicky2 comments. It's by far the "deepest", but has its share of issues which need to be resolved if/when they do Vicky3. The biggest problems, in my opinion, are:
1 - The top GPs get first pick of as much as they want to buy on the world market, rather than first dibs on it up to some percentage, so countries not a lot further down the list may get NOTHING, no matter how much they're willing and able to pay. The real world doesn't work like that.
2 - Transportation costs aren't considered, so it's no cheaper to buy bulk items like wheat from the farms in your own province than to import it from the opposite side of the planet, which was certainly NOT the case in the 1800s. Transportation wasn't free, and the price difference between sources had to cover the cost of transporting the goods, otherwise you'd buy it from someplace closer.
3 - The amount of money in the economy doesn't increase at nearly the same pace as consumer demand for products (which grows by orders of magnitude), so your pops are unable to purchase everything they need in the later stages of the game, almost entirely due to the lack of capital to cover the sheer magnitude of daily purchases.
4 - There are NO stockpiles, so anything produced and not sold that same day is simply lost. Nobody bought that state of the art airplane or automobile today? Scrap it! Storing up a year's supply of everything, like in HOI3, is silly, but the real world definitely maintains some stockpiles, as well as goods in transit, amounting to at least several weeks worth of goods.
5 - Workers are paid a percentage of profits, so if the goods don't sell that day, there are NO profits, and the workers are unpaid, meaning that they have no money to buy other items on the market. This can lead to a snowball effect, and the closing of factories where there's insane amounts of demand, but no money to buy the products.
HOI4's production lines and "equipment" are a step forward from HOI3, but the series really doesn't do any semblance of an "economy", and HOI4 removing money from the game doesn't help. I can't speak for EU4, but EU3's economy was rather rudimentary at best, and the only thing that mattered about trade goods was their cash value; it didn't make much difference in price, no matter how much you sold of a given product in the same market region. Sadly, I think that Chess has almost as good of a trade system.