'Dark Congress' isn't the best of novels, but, shipping preferences aside, it's A LOT better than 'Queen of the Slayers', the only other novel to be set post-S7, and I think that's because it doesn't try to shove itself into the canon.
'Queen of the Slayers' tried SO HARD to line up with the canon that was created in the Angel episode, 'The Girl in Question', that it looks nothing short of ridiculous now, seeing as how TGIQ was retconned to the highest degree possible. Even the episode itself seems a little stupid now.
Everyone in 'Queen of the Slayers', though, seems completely out of character, most especially Kennedy. There is no way that she would act the way she did in this book, and I think that really got to be more than the ridiculous ending.
'Queen of the Slayers' upset me greatly, because Nancy Holder is one of my all time favorite BtVS novelists, and for her to come out with something as bad as this was honestly hurtful. I'd advice EVERYONE to stay far away from it.