The art improves as the series goes on. In the beginning, it could be a bit busy--with the backgrounds and foregrounds not being immediately distinct--but that seems to have become less of a problem. I don't really like Ainz's character design in general--with his exposed ribcage and box-y silhouette--but I can notice that there have been some slight improvements to that as well. Like, they've gotten better at drawing his skeletal face, so it doesn't look as sunken in. And they've stopped drawing him in the flattened chibi-form, which didn't look very good.
The strongest point of this manga is the characters. There are quite a few really cool subordinates working under Ainz in the Great Underground Tomb of Nazarick. And so far, several of the story arcs can be seen as showing how these subordinates have changed from being thoughtless NPCs to having their own motives and priorities. There's a brief storyline following Shalltear, the true vampire, which is mainly used to show that there are people out there who could even threaten the overpowered members of Nazarick (ch. 10-14). Then there's a story about the conquering of several lizardmen tribes, largely shown from the perspective of the lizardmen, meant as an exercise to teach Cocytus and the other ex-NPCs in Nazarick to be willing to think for themselves and question orders (ch. 15-27). Ainz's followers are all too happy to ascribe absolute genius to him (which can lead to some pretty funny moments and misunderstandings), but he tries to instill a willingness to brainstorm with him rather than just blindly obey. Then there's a storyline involving Sebas and the internal tension between his budding desire to care and love for a human woman and his belief that all his actions should be for the betterment of Nazarick (ch. 28-40). This section introduces several human figures within the political and adventuring scene of Re-Estize's capital city E-Rantel. The most recent story arc involved an attack on E-Rantel by Demiurge's forces, which acted both as a way for Ainz's "human" alter ego Momon to save the day and as a step in the goal of world domination (ch. 41-52). You see, Demiurge believes Ainz wishes for world domination because of a passing remark he had made back in chapter 2, and at this point Ainz just feels it's easier to go along with it.
I do enjoy a lot of the character designs and their characterizations and I think that it was the right choice to focus the various storylines on different characters, but the stories themselves don't really capture my interest all that much. The first few chapters (up to ch. 9) are just introducing the world and characters and showing how dominant Ainz is compared to average people. Since it's still fresh and new, it can be entertaining, so I don't have many complaints at this point. Then there's the fight against Shalltear and that was a nice breath of fresh air since it was an actual challenge and there was the possibility of Ainz losing. But the choreography of the fight with all its consecutive high-level moves we're seeing for the first time made large swaths of the fight gloss over me. Then with the lizardmen plot, I didn't really get invested with any of the lizardmen and the fight itself seemed dull and empty. As for Sebas's plotline, I found his interactions with Tsuare to be cute, but I didn't really care for the meat of the story--for Climb and Brain's involvement. Similarly with Demiurge's attack on E-Rantel, I found Evileye's crush on Momon (Ainz's alter ego) to be adorable, but the fights themselves didn't really engage me beyond some minimal amusement at how much of a farce it all is. There aren't enough chapters in the current story arc to really know how I feel about it yet.
[Reviewed at chapter 54]