I wholeheartedly endorse trying out Uncharted Waters 2, and not just because it is one of my favorite games.  It’s not too difficult to get into with understandable concepts like buy low sell high, death and taxes, sail the seven seas and without much in the way of weird language to learn.  The most difficult part of it is figuring out how often to save since you can easily lose an hour or more, leave yourself in a bad situation, or outright soft-lock your game, but save states eliminate that.  Guides are available now which should flatten what learning curve it does have.

The game itself is a mix of trading simulation, exploration/strategy, and a little Age of Sail naval combat.  While I wouldn’t rank it as best in field in any of them, I think the game is a prime example of one that is greater, much greater, than the sum of its parts.  If it happens that one of the elements doesn’t jibe with someone, they can drop it and still have a great time.  I think you can even have a good time focusing on trading or exploration exclusively.  This doesn’t mean as much today as it did in the pre-internet days, but there is also a lot to learn about the world (though much of it is grossly unhistorical being in the time period).  I could easily get manifesto-ish on how significant the game is and why people should play it so I’ll leave it here.

I wouldn’t say Nobunaga’s Ambition is impossible or inscrutable since I beat the campaign when I was 12, on a weekend rental, without a manual, and as my first Koei game of the type (Aerobiz Supersonic was my first but it doesn’t do much to prepare you for NA).  That being said, in my defense:
It was pre-smart phone so before the annihilation of the attention spans of people in general and kids in particular.  I pretty much played it nonstop over the weekend.

Strategy and war games have been my favorite genre since beating adults at Risk when I was 7.  I was also already familiar with a good deal of the terminology and concepts from books.

It is certainly very difficult or very, very difficult (maybe very, very, very difficult) without a manual or guide.  That being said, there's no reason to play it even with a guide except for nostalgia or as a historical curiosity given Shogun 2 exists.

Koei has a few more games than the Aerobizes to put on the service though not much reason to.  I've played all of their SNES games except the RPGs Inindo and Brandish.  Gemfire and Genghis Khan are NA/RotTK in a different setting.  PTO 1&2 were great at the time but any modern Pacific War game is a better choice.  Operation Europe was trash as a wargame even at the time.  Civilization was published by Koei, it would be cool to me for nostalgia reasons but I doubt they still have the license and FreeCiv is available and, well, free. Liberty or Death is the only good choice as there aren't many AWI games, oddly, and it is actually still one of the best AWI games I've played.