You guys keep arguing about the "demon lord/magic king" naming and I'll be here defending the real demons real quick.
Honestly, I don't get why the manga has such a low score (to me; I'd rate it at least an 8 for MAL but it's actually a 7). Cliche is not a good reason to talk bad about a story. Look at My Hero Aca as an example. He said that he's the number one hero from ep one yet we keep on consuming each chapter with delight. In other words: it's not about the ending but rather the journey.
Yeah, all the demons seem to have the same motivation of 'revenge' but all you guys are seeing their plans and not their actions. I say that you better see the ending before you judge it. I personally love this series just because on their unique theme of "antagonists are also trying to live their own lives" that isn't really seen much elsewhere.
You could argue that new =/= good but at the end of the day this whole thing is experimental. So let's just stick onto this roller coaster amd see where it takes us, shall we?