Well, I'd say that this game managed to present more of a 'forbidden fruit' feel to it. It opened better than Maid to Please, it was more exciting. In Maid to Please, the father's wife is a little bit corrupted in the foundation of her character. I guess between the two wives; the one in Maid to Please and the one in My Brother's Wife, the wife in Maid to Please is the lower hanging fruit.
However, over time, My Brother's Wife lost its edge and Maid to Please did surpass it, in my opinion. And quite handily, at that.
This game had the initial advantage because, at first, you were seeing the brother's wife being seduced out of her character by all the circumstances involving her and the MC. To clarify; it felt like she was being just swept along and it felt dangerous and exciting and definitely beyond her conscious control. I don't know if Maleficent even realized how well he had created that opening dynamic and I see other game developers actually consciously trying to achieve precisely the same, with limited success. That is why this game was so popular initially, that was the reason it captured a large audience. It hit a psychological button which elevated the perceived value of the brother's wife as a forbidden prize for the player.
It's actually a little bit sad to see what happened to it, from a creative point of view.