Yeah the start does take quite a while to get going. It’s just opened up for me, at least for Naoe. I found in some of the initial bits I wanted to try and take everyone out, but it was more set up for you to sneak through.
One early recommendation I’ve seen is when it does open up concentrate on your first two assassinations, rather than exploring too much, as that will progress the story to include Yasuke. That means you’ll get loot for him as you wander around too.
It is a really beautiful game. Very different stylistic approach to GoT but impressive in what it does. Density and variety of foliage is particularly impressive.