Before going into what i think about Yuria 100 Shiki, i think i need to make it clear that i watch/read both hentai and regular romance, so this opinion is coming from the perspective of someone who likes both. Another thing i need to admit is that despite having 'completed' this manga, i did skim through the lolicon shit, i just couldn't stomach that part of the manga. That being said, lets get started.
Going into the manga, all i knew that was it was about a perverted female character, and nothing more. I thought it might be a good ecchi and might make me laugh a bit, but what i got was an experience that was much more character driven than i expected, There were actually some characters that i liked and cared about, examples being Juria and Yoshio. Their relationship is probably the only thing worth reading for. Unlike the main characters, both their characters and their relationship have a little development. Thankfully, the chapters focusing on them always came at moments when i was ready to put the manga down because it got boring. Juria and Yoshio were interesting enough to keep me reading, even when the primary characters bored me.
At the start, Yuria and Shunsuke(the main characters) seemed like they would have an interesting dynamic. I liked the idea of a character who wants to be innocent but ends up doing dirty things, and i thought the love triangle element could have added something to that. For the first 20-30 chapters, i thought they were on the right track. It was a bit slow paced, but the comedy was still fresh up to that point, and the ecchi scenarios weren't totally played out yet. It seemed like they were slowly developing the relationship between Yuria and Shunsuke, and also establishing the relationship between Shunsuke and Maria. The problem is that the manga fails to capitalize on this potential. By the midpoint, the comedy became stale so that wasn't keeping me reading anymore. One might argue that the manga is a comedy, and therefore does not need to capitalize on its romantic potential. I would be inclined to agree if it werent for the fact that the manga also had moments when it took itself seriously(all of the moments where Yuria is contemplating her love for Shunsuke, also moments where Maria tries to kick her out), so i dont think the fact that is a comedy can be an excuse for failing in this regard. Its obvious that the manga wants the reader to care about Yuria and Shunsuke getting together, which just further shows the focus on the romance. If it didn't waste so much time focusing on the romance, in a non-comedic way, then it would be forgivable.
As far as characters go, they are a mixed bag at best. We are supposed to like Yuria and root for her. She is an innocent character(as in, she doesn't have malice in anything she does, and she doesn't want to be perverted despite her programming) who is trying to do the right thing, so she is likable. I think the problem with the whole dynamic of the story is that it is hard to like Shunsuke. The whole idea behind his character is that hes a nice guy who is also loyal to his girlfriend. He is so loyal, that he is turning down the sexual advances of these sex dolls. Sounds at least decent right? Well, the real problem is that despite these sexual advances, he actually lets one live in his apartment with him. Right there is a problem, i dont care how nice you are, you do not put yourself in that situation when you are in a relationship with another girl. Well, lets assume for a second that this is really the nice thing to do. Well, its fine then as long as he turns down her sexual advances. The problem is the fact that he allows her to grab his dick, and he even basically has sex with her on more than one occasion(and even tries to hide it from his girlfriend, because all he was doing was trying to be the nice guy and help her out). This would be fine if his failings in loyalty were actually punished, but they never really are. Personally, i dont think the whole 'hes so nice that he is willing to do this' is a defense for most of what he does with Yuria. He is way too calm about it when its over, and he doesnt even seem to care that he might have cheated on his girlfriend. Maybe this is a point that wont bother people, but this type of 'nice' character is just the kind of character i can never buy into. It takes me out of the experience. In harems, and other love comedy anime/manga, the main character at least feels embarrassed at one of those kinds of scenes. But Shunsuke is so boring that he just immediately moves on from it. This should be fine though as long as its funny right? Initially it is funny, because it defies our expectations of how a normal person would react to it. But its not the kind of joke that can be repeated for over 100 chapters and still be funny. By the end of the manga, the whole dynamic ceased to be interesting because the center of the love triangle was this boring guy that no longer made me laugh and wasnt likable either because of how much he basically cheats on his girlfriend.
The other major issue with the manga is all the side characters aside from Juria and Toshio(again, they are what kept me reading). Yurin is a loli character, and there isnt a single chapter that she was in that didnt bother me. To the mangas credit, I did enjoy a few of the interactions between the three sisters, Yuria, Juria and Yurin, despite hating Yurin. Im not a fan of lolis, especially not ones in manga such as this. The hermaphrodite(whose name i honestly cant remember) was just such a throw away character, even the loli contributed more to the main story of the manga. There is also Lucy, who is also really boring. By the time they introduced her, the comedy was already getting dull, so every comedic scene with her failed to get a laugh. To the side characters credit, i dont think we were supposed to actually care about any of them(again, except Juria and Toshio, though im convinced the only reason they got development was because they were introduced really early on). The side characters were mostly just filler characters who didnt really contribute anything to the story, and only served to interrupt the flow of the main story. Even the comedy in chapters focusing on them was boring because they just repeated the same comedy as the chapters with the main characters.
The pacing of the manga was pretty consistent until the end, where they just went with a time skip and resolved everything within 2 pages. It was disappointing, the one thing Shunsuke had going for him(as far as character development) was his slow realization that he didn't want to be in a relationship with Maria, but they threw that out the window in the last dozen chapters. I think that was a big issue with both the story and Shunsuke himself. The love triangle only works if we fully understand where each girl stands in his head. But by the end of the manga, i still was unsure how he truly felt about either of them. Sure, he said a bunch of times that he loved Maria, but based on their interactions and the tension in their relationship(also the fact that for a while he was clearly leaning towards Yuria, because she was always supportive and there for him) i assumed he had enough with Maria. When the wedding happened, and Yuria had to be the stand in(yes, it is as stupid as it sounds), i assumed that was going to be the moment where he realized that Yuria was the girl for him. But instead he kind of just decides to be married to Maria anyway, despite seeming unhappy with her, and has Yuria stay with them despite this? Then there is a time skip and Maria and Shunsuke ended up getting a divorce anyway. What the fuck was the point of the part where he decides to stay with Maria then? The entire manga up to that point was building up his frustration in the relationship, and his potential love for Yuria, if any time was good to have him dump Maria, it was right after the wedding. The whole ending being right after a time skip resulted in it feeling rushed and poorly thought out, despite being a simple one. .
The bottom line is that this manga isn't really worth reading for anyone. The comedy is funny for the first dozen or so chapters, but it gets stale by the halfway point. The sex scenes are more censored than most hentai manga, and they lack any kind of detail, so anyone looking for sex scenes wont be satisfied. The romance is poorly thought out and really falls apart at the end, so anyone looking for a good love triangle story wont be satisfied. This whole manga just fails to find an audience, on one hand its an ecchi with tons of sex scenes that lack detail, on the other its a half baked love triangle story with mostly shallow characters. If you are looking for porn, read hentai, if you are looking for a love story, find a different manga. I would be lying if i said i didn't at least enjoy some of this manga, but it was still a let down.