Maybe if I hadn't read Peter Ellis' Cadfael series (although I haven't finished all the books yet) I would have liked this book more... I don't know.
Maybe if the lusty, blaspheming dowager Lady Ermentrude was not so an anachronistic character, or if it didn't take more than half the book for Sister Frevisse to realize that said lusty dowager and some other "innocent" victim were in fact very obviously poisoned, or if the poisoning symptoms weren't so singularly described that at first I thought that the poison used was Monkshood instead of the poisons that the author names later (which symptoms are not exactly the ones described either), I wouldn't be writing this.
And there are more things that bother me, for example the fact that the author makes it purposefully obvious that the wine was use as the administration method for all the poisons, and then for a twist in the plot, makes it impossible for the wine to be poisoned, but NEVER explains later how the poison was administered! But hey! Don't worry about that! She will still use the poisoned wine in the frantic climatic scene where we learn that indeed the wine was poisoned!

After writing all this, I think I actually didn't like this book.