Poland and Muscovy have hella lot of unique events, like 40 - 60 of them each - I counted countries with the most unique events once and these two were high.
Lithuania has like 20 of them.
Poland/Lithuania => Commonwealth and
Muscovy/Russian minor => Russia offer very distinctive gameplay. Russia is about colonising Siberia and dealing with European and Asian countries at once; Commonwealth is about extremely tolerant multinational country with extremely powerful cavalry.
Also: Commonwealth has its own unique government type, Elective Monarchy. As Commonwealth you can be Catholic, Protestant or Reformed country, while Russia is one of few Orthodox countries in the world and has Patriarchal mechanic.
These countries are the most developed as they are the biggest here, but there are many cool nations here:
- Bohemia
- Livonian Order -> Courland
- Ruthenia (well, first you would have to release it from Lithuania)
- Now every single nation in Balkans except Transylvania has its own unique ideas. Croatia - trade power, Bosnia - tolerance, Serbia - strong cavalry army, Wallachia - strong infantry army, Moldova, Montenegro, Bulgaria (releasable), aaand there is Albania for absolute hardcores.
Personally I don't recommend Hungary as I had very frustrating experiences with it, and I am not alone here
