I just got through Chapter 1 and had a blast. While reading up on some other aspects of the game, I came across others having difficulties with the abghoul and the Beast. (I haven't heard too much about the big drowner. He was pretty easy.) I didn't read what the specific issues were, just headlines like Trouble with the Beast! sort of thing.
I was ready for really tough fights, but was let down, so to speak, by how easy they were. All I did was hit them both at the beginning with Aard. They were stunned, and in one hit they were killed. Did I just get lucky, or is Aard that powerful? I'm playing on medium, and I did power up using a place of power before these fights. Anyway, for those having problems with these two, try Aard.
[spoiler]Chapter 1 trophy monsters
It was undoubtedly your powered-up Aard that won the battle for you. I used Aard but could never get the Beast stunned long enough to do a finishing move, so I just whittled away at him while ignoring the green barghests. The main problem with Beast I think his incineration effect, meaning you stand there helpless while clutching your burning face and screaming. I have also heard that the fight was made much easier in the Enhanced Edition; I only applied the EE patch after I beat Chapter 1 so I can't say for sure.