Thinking I'll give MEIOU & Taxes a shot. Anything I need to know that the wiki fails to mention?
Playing as most minors outside of the HRE, Italy or China really sucks. The population mechanic makes it so that small nations absolutely cannot play tall, they will be crushed if they cannot expand or get the required income to increase education and outfit a small, elite army. The problem is there are very few nations which can afford these expenses, while expanding is for most nations going to be slower than playing as Jains in CK2. For example in Anatolia there are numerous minors, from the Romans, to the Serbian Empire, to the Crusader States, to the Anatolian Beyliks and the Merchant Republics.
However none of these states will ever be able to expand, because in the time it would take for them to field an army and annex any of their neighbours, the Ottomans will have become a world power and destroyed them. This is because MEIOU & Taxes likes making more historical outcomes, which is really nice when it is from simulating the factors which resulted in such a rise - but not so fun or interesting when it is just one tag having less mechanical barriers than other states. Thus while I played Ottomans I quickly annexed everyone with no trouble, as I had access to a CB which gave me claims to everything and allowed me to annex everyone with 0 AE using war dynamism. Most states could not survive a single battle against me, and I grew incredibly quickly. Upon expanding to Ottoman's historical borders however, I kinda just got stuck there. Conversely while playing as Knights, I found that I struggled to outfit an army of 6,000 men without breaking the economy. Improving Rhodes was impossible, while my economy depended upon two land based cities. This forced me to go on the offensive, but I quickly found that while I could win many battles with my small, elite fighting force - I could rarely conquer anyone, as touching two provinces would spawn a coalition, and it usually took years to get a CB. This contrasted with the AI Ottomans who were rolling through Greece and Anatolia with absolutely zero limitations.
You might think there may still be some fun in the challenge, of waging a long campaign against such an asymmetrically favoured foe - one which can just claim your territory and annex it while you're fighting, while you cannot do the same in reverse. But, if the game isn't crashing every year, even the most powerful enemies can be destroyed by running a highly-developed, well-defended (in this case, by my navy), educated state, fighting to kill the enemy, not win. Once they run out of manpower they have to hire mercs, but with loans starting off with 10% interest, it doesn't take long for the AI to max out on loans and bankrupt. This led to the rather disheartening scenario where I could defeat the gratuitously large Ottomans and Mamlukes whilst barely keeping my economy afloat, but I couldn't afford to take any provinces from them - whether it was because I couldn't afford the AE, or I couldn't literally afford to hold the province.
Playing as a European or Asian state that isn't in the firing line of a historical power however, the game comes into its own as just dank beans all round. One of my most fun runs has been the Papal State - making that most difficult climb of returning to Rome, annexing the vassals and playing a complex diplomatic game towards unifying Italy. It gives you a hell of a lot to do in peace time, in administration and development, and is really where the game absolutely shines. Communication efficiency, population encouragement and estate management is the game's bread and butter. You genuinely feel like a sovereign Dorf Fortress overlord managing a state, in the sense that you are not making things happen - you are telling people what needs to be done, and hoping they implement it well.