I don't know about others, but for me it's in that he nails the typical "japanese milf" lifestyle perfectly with yes, slow corruption and amazing art/writing. A lot of VNs and games don't do well because they either have too little/much writing, or too bad/good art in wrong sections. I'm talking about games that either go straight into the sex after like 1 minute of introducing characters, or the games that just have terrible writing and bad art like giant ass dicks and tits that are bigger than the heroine's head. Here are his unique elements that other VNs fail to do:
-Art is proportionate. NTR is more exciting if we can relate to it better on an emotional level. The characters have good emotional investment while not being too long so you're just sitting limp the entire story. You can actually think of it like going through a well written anime.
-Sexting. This is probably his most famous element in that he introduces "suspect" NTR. You won't be able to see the full picture until you finish that story. You can see partial and it's really exciting to see that the wife is literally cheating and being corrupted at the same time. PoV is way closer than you think.
-Writing is excellent. While it's not too lengthy, it's not too short either. Remember, the best part about NTR is the NTR itself, we don't really give a fuck about other things.
-Different PoVs (point of view). You can see it through the husband's eyes (sort of), the son's eyes, the seducer's eyes, and the heroine's eyes. Really gives a different taste in writing each time so you're not bored.
-Voice. I can't emphasize this enough. VNs need good voice. And help to god half of the NTR games make the heroine sound like either a screeching baboon saying "IKUIKUIKU" for like 5 pages or the tone of the voice is so boring you can tell she's reading from a script line by line. I'm not saying it's perfect, but it's very well done for this genre.
Overall, his milf games are the best hands down. I've tried his other KEmono games and they're just average due to bad voice and boring story. I think he knows that his milf games sell the most so he's starting to make more and more of them rather than his previous games in the past.