I have no problem with redemption story, my favorite on going series is Fairy Tail and they redeem bad guys all the time, so you know where I am coming from.
But I hate how they do it in this series. There is no build up, it just happens. Almost every villain, shows no signs of character depth, they are just two dimentional villains, than when it time for redemption, they all of sudden have character depth. Sometimes even within a episode. Nephrite went from having nothing but destain for Naru and than one scene later all of sudden he has feelings for her.
Ali and An wanted to suck the enegy out of babies, and than they have feelings beoynd just selfishness, the Spectre Sisters showed no sign of any sympathic qualities, until it was time for them to turn good, even within the redemption, in Berthier redemption episode, Petz and Calaveras were so awful to her. And so on, they improve later on in later seasons, but not by much, the Amazoness Quartet weren't terrible heartless people, so that is a start.
That is not how you do redemption stories. Yes you introduce as straight out villains with no sympathy and redemable qualities, that is step 1, step 2 you slowly show some signs of sympathetic quality and / or show some signs of a good side, step 3 you mix up step 1 and 2 for a big, step 4 you redeem you character.
The way Sailor Moon does it, they start with step 1 and stick until the last moment, and than go to step 4.
It is like in Avatar: The Last Airbender if Zuko was more like Azula or even Ozai until he redeemed himself.