Everything about the game itself is a definite 5, the everything else kinda lowers the rating.
This game has LOTS of potential, despite all odds. One wouldn't think that there would be something left to do in the super-vanilla-incest genre, but apparently one would be wrong.
A setup that actually makes some sense (enough for suspension of disbelief to kick in), hot models (even if all catering to your classical body preferences - fit, slim waists, significant tits) and very high quality of general renders, and although the humor does give me some Waifu Academy flashbacks, it's nowhere near THAT bad. The game has hot situations and writing, decent characterization given to all girls, and just generally the author's experience is apparent. I even like the slow burn start. If the game ever capitalizes on what it has set up for itself, it will definitely be among the best porn games out there.
The metadata, however, paints a much bleaker picture.
The writing in the game smells... A bit cheap to me. It is great, don't get me wrong, it's just that I see this "mystery" setup, the "oooooooh everything and everyone has deep mysterious problems and we gotta get to the bottom of this!" a little cheap as a trope. I feel like I'm about to get Sherlocked, if I may use that word - the mystery will always just kinda be there and its resolution teased, but those teases will never be delivered on.
While I previously said that I like the slow burn, I meant it in terms of the story, not in terms of the development process. The game has been in development for almost a year now. In that time, we only barely finished the exposition. I don't think we're ever getting actual sex scenes from this, let alone any advancement in the story.
And the last problem, that complicates the previous one, is just how overloaded the author appears to be. He has 2 games in development already, and plans a third. That doesn't sound promising to solve these problems.
So, Secret Summer. A great take on a tried and tested idea, with an incredible execution, being led down by the author. A genuine tragedy, really.