First a disclaimer, I haven't read the manga so I'm looking this from an outsider point-of-view. The concept of placing a high-level level RPG player into a "real RPG world" is interesting but many of the characters are just too weird for my taste. I enjoyed all the human characters in this anime but most of the characters from the Great Tomb of Nazarick are too hard to relate to.

The main character is a skeleton with suppressed feelings (taking away the feelings is a strange choice, it makes the character hard to identify with). Even the main characters name, Ainz Ooal Gown, was stupid. And what is the point of having succubus if you can't even have a boner (pun intended). There were also other weird characters such as insect humanoids, trans children, nazis etc.. The only interesting character from Nazarick was the demon Demiurge.

The motivation for Ainz Ooal Gown's world domination was also not clear. It's hard to explain motivation if the main character doesn't even have feelings. Also, I don't understand why the show wasted 4-5 episodes with the lizard-men. At that point, it was already clear that the characters from Nazarick are so OP that there is no strategic advantage on making them your allies. And I was right, the lizard-men were totally forgotten after their introduction and they played no role in the rest of the story.

Still, the show was not a complete loss. Afterall, I watched all 4 season. I just wished they had concentrated more on the human characters and made the task of world domination a harder strategic challenge.