You get to spend 30 days with two beautiful cousins and an aunt. You get to do all sorts of things with them... like collecting bugs... fishing... washing dishes... completing your math homework... stuff like that.
You also get to release your white pee from your weewee while at it.
The story is not really complex. Plays more like a time management game than a visual novel. Of course there are some events that you'd expect from these games, like going to the beach or hiking, but this game is not about the dialogue or the story.
The game has some cute, slightly pixelated graphics, which give it a very nice vibe overall. There aren't that many unique CGs in the game. Most of the deed is done using the basic character sprites (either the version seen in dialogues or the the version used on the map/rooms). So, it's more of a question of which color girl you want this time, than anything else.
All that said the game itself is animated, which makes recolored content a bit more acceptable.
Finally, the game is a nice pick if you want to be pampered by busty onee-chans all during your summer break. There are a lot of activities you can do, which all work towards improving your relationship with each girl and as such, there is a sense of progression. Some of the features may be confusing at first, so it's highly recommended to read the tutorials. The 30 day time constraint is not too tight, so even if you take some time to figure things out, you can still unlock everything in a single run. The game offers a good 10-20 hours of playtime.
Have fun!