I love the idea of them, but most of the time actual routes with incest fall short of my expectations, whether blood-related or not. I yearn for toxic codependency between family members that doesn't rely on it being seen as forbidden by the characters themselves.
I'm going to take this chance to hate on a trope I constantly see in media with brother LIs. The contempt I have for any brother LI who sleeps with people who look like or remind him of the MC—and then the MC is a beacon of purity who has never even kissed someone... I'll actively root against an LI like that.