Absolutely gorgeous game. It really encapsulates what summer vacation feels like as a kid, complete with the freedom and aimlessness and melancholy. I can't recommend it enough.
In terms of Japanese learning, it's an excellent game to learn from - every line of dialogue is fully voice acted with subtitles on the side, and since you're playing as a child the conversations are generally simple. Also, since there's narrative arcs that hint at deeper things that a child might not understand, you still get a sense of complexity.
Since the game takes place in August and is separated by each day, I played "alongside" the protagonist all month, playing one day in-game for each of my real-life days. Hence, why I finished today on the last day of August. IMO this is such a good way to play the game since it feels less repetitive and more like you're checking in with the protagonist's adventures every day.
Anyway here's some random vocab words I picked up while playing:
潜水士(せんすいし):(professional) diver
窮屈(きゅうくつ):constrained; narrow
稚魚(ちぎょ):fry (baby fish)
物知り(ものしり):(someone with) extensive knowledge
燥ぐ(はしゃぐ):to be in high spirits
線香花火(せんこうはなび):sparkler
下心(したごころ):ulterior motive
蜻蛉(とんぼ):dragonfly
浜辺(はまべ):beach; shore
夏バテ(なつばて):summer heat fatigue
岩礁(がんしょう):reef
夕陽(ゆうひ):setting sun