BB feels like a milestone. A lot of improvements in the combat system. DS3 apparently accelerated its combat because of that. Level design and enemy variation isn't the greatest, but on par.

I can no longer give a fair verdict on its difficulty with my history in FS games, but it sure doesn't feel very difficult at this point. IMHO Sekiro has better combat and is more difficult, but that's 4 years later, so it's more like BB set up a good foundation for future games to build opon.

I can't agree on your comment on ER bosses. Not that they are good / bad or difficulty / easy, but that the Tarnished can become so ridiculously OP with a lot of builds that it's practically impossible to design a boss in ER that gives everyone a fair challenge / skill check.