My problem with the One Sith era is with concept. From what I've heard its actually a pretty kick-ass series and shaped itself into a respectable part of the mythos. But man does it take a dump on Luke and co. The order, freedom and peace that they worked so fricking hard to create and preserve is just completely undone inside 1 or 2 generations and the Sith control the galaxy again. Its like everything Luke did to fight the darkside was completely pointless.
But of course most post-Endor stuff is guilty of this. After the collapse of the Empire the universe kind of went to shit. It really puts a damper on the ending of Jedi knowing how many wars and how many trillions would die in the following 40 years.