I don't think it's unfinished as in NTRMAN releasing it and putting aside stuff s/he wanted to do.
Rather, I'd say it's that good we actually want more of it. Well, whatever the case, I really wish NTRMAN would make extensions/addon whatever-it's-called, I doubt though s/he has that planning nor if people actually asked for it.
Well I kinda felt NTRMAN, maybe wanted make the game a bit bigger with more mechanics. Do you remember that you had choices in the conversations? The characters kinda reacted differently depending on your choices, but it eventually led to nothing. And in the end there were only 3 endings. The good ending where you avoided NTR (my personal favorite), bad ending where the both characters stayed on the Island and the last gangbang ending. I hated the gangbang ending the most though, because the game actually teases a harem ending and it ended up also nowhere, instead you get the worst ending for the male character.
Also storywise, the male characters are putting their love ones on the line in those challenges. The main character had his wife, the head of the village has his daughter and that buff dude also has his daughter. But that kid with the boat challenge had nobody, so why does he get do to the challenge without anybody on the line. I would like to request NTRMAN to design a MILF or an older sister for that kid and expand this game further LOL.
So yeah, these are the mean reasons I feel NTRMAN intended to make this game bigger. What do you guys think?