The main issue with BB, at least for me, is its poorly implemented hub area. I feel most Soulsborne games since DS1 have digressed in the lack of being able to conveniently do everything at the bonfires. Having to constantly go back to the Hunter's Dream to repair your stuff and just to travel from one location to another becomes awfully annoying when you're going through two loading screens in quick succession.
Another thing is just how static and boring the hub is in general. Hubs in other Soulsborne games change over time as you progress the story itself and the individual stories of characters. In BB? Nothing changes besides the music, the doll changes locations, and Gehrman sometimes appears to spout uninteresting exposition. Nothing interesting happens on the Dream whatsoever.
Overall, it's just one big inconvenience you have to deal with the whole game. It's a mystery as to why DS1 did so many great things that just disappear in its successors.