Personally I found the boss battles weren't really like boss battles you would find in a platformer. Bosses don't have increased health or anything (apart from tartarus's shield) and I felt the battles were realistic and were actually what would've happened in the story. For example sesa refumee has the same health and shields as a normal heretic elite, Tartarus would have those shields because he is the chieftain of the brutes, and regret is a prophet so he understandably has an over shield, but he is easy to kill