It's a very solid game for what it is. Has a similar vibe to the Knightess Whore game. It took me two hours to reach the point where the blond princess has actual sex for the first time, and I disagree that there was too little build up. And yes, the game is mainly about cuckolding and the main character will peek at the scenes. And yes, the green haired girl isn't NTRed, so her scenes are more about envy than jealousy, though IDK where the plot will develop later. Surprisingly, there's also a rather touching scene with the first NTR-guy, who's Rance wannabe (no homo).
I already got used to people underrating Japanese games unless they have solid gameplay for some reason (even though English-made games usually are just visual novels and still get good ratings, lol), but reviews are too harsh imho. Story so far has some thought put into it, and the main characters have more depth than usually. Build-up with the blonde girl definitely was there, and while it wasn't that strong, the game compensates it with very solid h-scenes. Yes, they are kind of long, but who stops you from skipping? And sex talk is really good when there are actual dialogues instead of just "noises".
In a nutshell, it's a porn-game where the MC watches other people having fun with the girls, including his "pseudo-gf" later in the story. If you aren't into it, then skip this one, but otherwise get ready for a treat as games like this a rather rare to begin with, let alone with such high-quality art and varied background moans.