I felt this game was going in a little different direction than typical NTR. First the blackmail wasn't going forever and Zack cunningly made the Blackmail look like a choice (at-least that's what Sophie and Amy thinks). And it shows that Felix isn't stupid, he is suspicious but his trust in his wife made him oblivious most of the time.
Though it seems Sophie is dumb but she isn't, in the last arc it's revealed she always wanted a Star Athlete boyfriend but couldn't muster up courage to do it; So she just compromised and settled with Felix; So when chance came she unconsciously accepted all the lewd terms so she can live her dream. That's why she accepted in later arc she is a cheating wife cause maybe she was always cheating in her mind but couldn't find any way do it in physical realm until Zack came. Other characters also don't seems to be stupid.
BUT in the mid-way of the story the only person who is smart, cunning, good looking, physically fit, recovers extra fast is Zack, with a little bit of superpower he may become Superman in the next arc. I know in NTR world everything revolves around the Bull but come-on.
All these new NTR games that has Male MC point of view tends to go toward the ending of cuckolding/humiliation exclusively; I don't have problem with it specifically but if it's a game with many endings at-least one or two can have a ending in his favor, maybe a sad one but still in his favor . And I strongly disagree with people who says that the wife/girlfriend don't get good/happy endings, I mean the good ending is good for them, the Cuck ending is good for them and the NTR ending is good for them. If someone becomes a addict and ends up in a remote village where they eat, sh*t, drink your dr*g then it may be absurd and sad from others view but from his/her view it's a happily ever after.
Hope the future arcs would be interesting.
In some things I really agree, you had some good moments, but if we take Felix, I don't think it's the cuckolded husband who accepts, he shows it by his distrust and how he gets angry if he sees something strange, it's true that he makes a mistake on too much trust of Sophia, Zack is a villain who goes beyond his looks, never mind that he was given a cock that atonically wouldn't even fit in a cow, but he uses that dark tender side of him towards Sophia which makes her a succubus, Zack he is intelligent, he understands that Sophia must use the tactics of a good, sad, polite boy to corrupt her, especially in sex, using kind words, he deceives the ignorant Sophia, I'm sorry, but contrary to usual, it is not the husband here who is weak and naive, but she is the wife, we know the rules between teachers and students on relationships, well, Sophia in every ending, doesn't win as you said, because when she finds out about it, if the game takes us to the recognized cuckold husband, she loses the job, it would be a scandal for the college, so no one could help her, and this is what she always repeats to Zack, she tells him to have more discretion, both so as not to be discovered by Felix, but also because she knows the consequences, in fact, in a speech, she says clearly, if the relationship comes out in the open, I'm ruined, Sophia knows it, but she's now addicted to Zack's cock, and about Amy, true, she tells him to have fun with Zack, but that it's just a sexual thing and for a short time, so much so that in the last part Amy, not knowing the truth, praises Sophia for having ended sex with Zack, be that as it may, Sophia will be the real loser in the end, true, now she is living her dream, her top moment, but how much this will really cost each.