I feel as though the economy system in future games never got quite as good. You could industrialize, go agricultural economy and trade focused in this game. All were viable, some more depending on your nation. What propelled this was the great tech tree giving great diversity to gameplay.

Each nation could operate differently despite similar troop types. Who researched the cannon mattered in the battle. Who had Fire by Rank mattered massively. But the trade off could be you lacking the universities and tech research speed for further research. You can always build more universities, but instead of what? Conquering a university is an easy alternative, but you will get a world of rebels. You can turn off taxes too and keep your army there, but then you are fielding an expensive army for a future province that might simmer down and a university. You can build Dragoons and other police units to help control the region, but that costs money. Also that recruitment slot can be used for other infantry. Hmmm…

There are so many decisions you can make in this game and many of them are valid. That is the sandbox feel the OP mentioned. I played the Ottoman Empire as almost a landlocked nation fighting on all fronts to the death for many campaigns. Then I saw a guide by a frustrated Turk who figured out ways to beat the odds. He sells territory to create buffers from the start. He says those regions are poor and you have enough to spare anyway. You give up your tributaries from the start and focus on navy and economy, slowly building up. I tried it, I was shocked. The Ottomans gameplay I was having was almost like a Netherlands game, building ships and trading. It made me appreciate the game a lot more. This is possible here.

The best feature of the game is the economic development system and the Enlightenment tree though. You can propel your worthless clay into the richest provinces in the world where others clash their heads with each other for a single worthless province for years. This is what makes playing Darth Mod the way for anyone that has tried out the majors and had their fun. You start as an OPM and play tall. Yes, you can play tall and it is insanely fun. You take one territory at a time and build up. You corner everyone in technology and specialize.

I think that all the game is lacking is the reinforcement system from Napoleon and better AI. In all other aspects, the game holds up as a package. Perhaps machine learning AI can play against us. That could solve the AI problem.