We definitely have a lot of good options to choose from. For me, growing up with the Tenchu series played a very big deal back in the day, especially tenchu 3 on the ps2, man I loved that game to death. And I kinda see Sekiro as the evolution of that formula, so it's a mix of nostalgia and quality there. Tenchu had that sneaking around bit too, it actively discouraged combat outside of boss fights. Sekiro had some of that DNA in the way its sneaking worked and in all the various contextual assassinations. My fav thing back in the day was going in the water and using a bamboo shoot to breathe and hide from people. That felt like the most ninja thing ever.My ideal ninja game will always be Mark of the Ninja, in terms of stealth and sneaking around undetected. As far as combat, I give it to Ninja Gaiden II Black. Though I completely understand why you give to Sekiro.
They're making a new Shinobi too btw, 2D sidescroller, that one looks pretty good too.