I loved it. It's lacking some clarity in what makes its protagonist tick, but that's probably deliberate and in practice I think it's being resolved by massive, terrifying evil. That's funny, by the way.
It's a standard "stuck in an MMRPG fantasy game world" story, but with the twist of a villain protagonist. Momonga used to be an ordinary salaryman playing a VR online game as an undead overlord with a fleshless skeletal body, dozens of minions and a Great Tomb of Nazarick. However the game servers are about to be shut down and the rest of his guild have all returned to their real-world lives.
Momonga stays. He loves this place. However the world doesn't disappear at shut-down time, but instead transforms into a New World where his money is useless and his computer-controlled minions have developed sentience. Momonga gives himself the following goals:
(a) explore the New World
(b) see if any of his friends are still here
(c) protect and rule his minions
These are sympathetic goals. We can hear Momonga's thoughts. He's a nice guy who cares about his people, who in return love him unconditionally and with utter loyalty. Their devotion is rather sweet, actually. They know that they're the programmed creations of what they regard as higher beings, but they don't have a problem with that and indeed are proud of it. They're also full of gratitude to Momonga for not abandoning them as did his fellow players. Only mind control could prise them away from him.
However they're also terrifyingly, hilariously evil. If Momonga suggests raising an undead army, they'll be ready with helpful suggestions on which village could be butchered for a handy supply of corpses. They see people as cattle, toys and/or food. (Solution Epsilon swallows people whole.) They'll say things like, "Lower life forms such as humans should bow their heads in wait and be thankful when their lives are taken." Albedo and Shalltear are both in love with Momonga (who can't respond, being a skeleton), but they also both have fanged demon forms whose idea of "play" involves multiple victims, torture and/or ordering the deaths of everyone in a huge area, unseen.
With Momonga's minions, there's no ambiguity. There's nothing they wouldn't do. They're bewildered when Momonga behaves altruistically and only cheer up when they've thought up an evil hidden motivation to explain it away. The least appalling of them is Mare Bello Fiore and that's only because he might let a tear fall while beating to death a hero who's been tied to a tree.
With Momonga, though... well, it's interesting. It certainly creates dramatic tension, that's for sure. He's a nice guy. He cares about his subordinates. This is obvious when we hear his inner voice. However it also looks as if inhabiting an undead body is doing things to him. He reflects in an early episode that he doesn't feel anything when slaughtering people, which is just the start of a slippery slope towards ever more lurid Villain Behaviour. He's sympathetic throughout, somehow, but bit by bit he's starting to be included in the comedy evil of his minions. The weird thing is that he'll also go adventuring, do heroic deeds and protect the innocent (for selfish reasons), but you really don't want to give him any reason to think that your existence might be inconvenient. You'll be scared in ep.7 when someone causes Momonga to ask, "Are you the only person who knows [X]?"
That's someone who likes and trusts Momonga, by the way. There are also bad people (as in "more evil than our anti-heroes") who are capable of killing characters you wouldn't have expected to die. Momonga doesn't necessarily object to the "being gratuitously evil" bit, but that's not the same as letting his enemies live. Being reduced to sizzling smoke and a stain is by far the less disgusting of a particular pair of deaths. What's more, even though our anti-heroes are ridiculously overpowered by almost all standards, they're going to discover that this world contains powers that can threaten them.
All this is awesome. I'm not sure if I'm entirely convinced by Momonga's contradictory psychology, but boy is it effective. He can fight one of his servants to the death and you won't have a clue what he's planning. Does he care about her after all or is he really and truly going to kill her?
I want more. I'm thinking of buying the light novels, or possibly their manga adaptation. (Both are available in English. I'm thinking of plucking up my courage and trying to read the original light novels in Japanese, of which this anime adapts vols. 1-3.) Apparently the light novels' fans say that this anime cut out important material, so there's that to look forward to. Apparently it was the top-selling light novel series of 2015. There are two movies coming in 2017, which will apparently be compilations that also have new characters and scenes. Not sure what that means, but I'll be looking out for them. What I really want, though, is a second season of the TV show.
This franchise could have gone wrong in all kinds of ways. All that evil could have been unpleasant. Our anti-heroes' power levels could have made it a wank power fantasy. Those things didn't happen. It's great.