This game epitomizes the impact sound design and music can have in creating a true atmosphere. That combination is the best part of the experience; aural reactions were always timely to what was going on in the story, really lending a sense of awe and intensity to the whole experience. The 2.5D art-style was also a nice touch. The game manages to blend those artistic elements in very naturally in a way which does not feel forced at all. The story arc is also extremely unique; subverting the Touhou expectation is always a plus in my book, and lends towards the humanization of the characters themselves. Putting these two in such a relationship is interesting on its face and not something I've seen before in other works with these characters.
I'm writing this review after one ending (which I think was the intended one), but I do have to agree it's not exactly apparent what I have to do to collect the other endings outside of answer differently on the final question, and the game itself largely being a walking sim makes it hard to replay back for all those endings, especially since you cannot skip read text or save in-game as far as I could tell. There was also some parts towards the end where the writing really could have been improved; particularly in environmental storytelling. I would have loved to have known what the poem in JP read in the cooling tower, for instance. (Though I do like that Maribel just has no idea what any of the Touhou references mean, it's very clever.)
The fact this was done in three days was also intriguing to me; it has a lot more polish than even our two-week Jam projects have. This is a very well put-together game which I think should find a lot of success.