It's really hard to tell the difference, but basically, Bloodborne is similar to Dark Souls mechanically, but design wise it's different.
-faster dodge + faster enemies = faster combat overall
-enemies have better movesets so you can't circle strafe them or backstab
-backstabs are harder to do, and you can't cheese them like before
-it's even less direct than Dark Souls. It sort of tells you where to go, but the environment design is basically a giant maze, so you get lost pretty easy
-even if you learn bosses' attacks, the thing that really matters is how you avoid them
In short, there are lots of small changes that make a huge difference to how it plays. I'm not gonna say that it's harder because it's a subjective thing. Also, hope I don't come across as a fanboy