I'll have to agree with you on Artorias of the Abyss. He very much reminded me of Guts from Berserk when he wears his Berserker armor.
One of my favorite bosses from Bloodborne would have to be Orphan of Kos. The atmosphere leading up to that fight was top notch. The boss was probably one of the hardest in the game but once you started to figure out how to fight him it was really quite exhilarating!