It's not just Madara fans that hate her. So far she's been pretty bland compared to all villains that came before.
But as a Madara fan, here are my reasons.
Madara has been mentioned as early as Part 1 Naruto, being compared to Sasuke and all of that.
Later on we see Tobi claiming to be Madara, using his name to fuel a World War.
And then the real Madara is revived and it makes sense that he was the one behind Obito because Obito pretended to be him and was turned from a nice kid to someone evil.
It was expected that Madara would be the final villain because his name was synonymous with evil. He also had connections to Sasuke since he is last Uchiha and Madara is one of the greatest, not to mention they were both Indra incarnations and the only ones to ever obtain the EMS.
Kaguya just came out of nowhere and was first mentioned about 10 chapters ago.