Holiday Island has a multitude of different options, random events and specialized encounters that are all part of building the relationships with each of the girls surrounding him. Just like in real life you will get hungry, horny, drunk and need to sleep. Just like real life, if the player doesn't interact with and pay attention to a girl(s), their affection, love and desire for the player will decline. This isn't a virtual novel where you skip dialogue until sex happens. This is a game where immersing yourself in the context, manage your daily activities and pay attention to the girls' tendencies, wants, desires, etc. will lead to various encounters and pay dividends down the line. The game isn't complete yet, but there's a lot of content to enjoy. As for whether there is 'grinding', the developer has already provided the best answer.
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Sounds like you expect this game to have a beginning, middle and end, along with having a format you prefer. Based on your post, Holiday Island will never measure up to what you want it to be. Take your comment on Aly as an example ... Yes, she was one of the first girls, but although popular with some players, her popularity pales in comparison to say Yvette and Amy. Just because she doesn't have a penetration sex scene, doesn't mean she's flawed. Sex with Aly will happen when it happens. Meaning when the developer decides to write and render said scene.
Read the above from the developer. There is no need to have your and the girl(s) stats maxed out. It will not help you if you're achievement hunting, which incidentally is the wrong way to play Holiday Island. The Companion Guide and other posts within this thread offer an easy solution to guarantee Yvette is in the sauna on co-ed days. The latest update even allows you to invite her to sauna.
Not saying your opinion or take on Holiday Island is wrong. Just suggesting you might consider looking at the game and the way you play it in a different light.