So I dueled Bhaal in Spellhold and after 4 magic missiles he is near death, and I'm like, sweet. 5 lightning bolts and 20 dagger throws later, he is still "near death" and going strong. I finally just let him kill me in supreme frustration. Is this typical, did I throw in the towel too early or was this the game F-ing up.

*------- Spoiler --------*

You have to make him follow you into the keep over to Imoen. She then makes is so that he is killable. Then you kill him.

All my spellcasting and dagger throwing was in the room with Imoen. I was basically running around and around the central squarish high-ground in that room (where she is standing) with haste-boots on and turning around and attacking when I had the space to do so and not get mashed.

that happened to me too. reload the game and do it again. its a bug in the game with papa-bhall.