Since I'm nearing the end (I think), thought I would chime in some general thoughts. Regarding the difficulty, I think it's just right. Sekiro has challenged me every step of the way, but never suffocated me with a feeling of insurmountable dread.
Honestly, it reminded me of my time playing Metal Gear Rising. I crawled my way through in that game until making it to the "come back when you can actually parry" Wolf boss and couldn't proceed for a full day. Eventually, something clicked and I was finally able to develop parrying skills. By the end of MGR, I really felt accomplished and skilled.
One minor pet peeve is the reused bosses and minibosses. This isn't really a new thing for FromSoft games, but it seemed kinda ridiculous this time around. On average, the bosses are okay to pretty good. Only two of them so far have felt truly special.
I was very concerned about the Dragonrot mechanic, but it actually isnt much of a big deal. Just spend your money/buy coin purses as well as reaching the next skill point level before studying a boss and you are good just dying without reviving until you have practiced a fight enough to employ the revives.
The environments and exploration are the real stars of the show for me. Discovering some awesome treasure or a hidden area always get me pumped. I absolutely love the Prosthetic Tools even though I barely use them. My last thing to say is that the Japanese voice cast really nailed it. I will try out the English audio for my New Game Plus playthrough, but I'm really happy FromSoft made Japanese the default audio option.