As an Isaac fan, this is a really great rebuild of the game in such a short amount of time and has some pretty solid gameplay! Also as an Isaac fan, I do find myself wishing it did a little bit more to separate itself from Isaac. While not the only example, I think the biggest offender here is the setting - Touhou isn't really known too much for brickwork and stone dungeons and while there was a short narrative blurb justifying it I just think it'd feel a lot more impactful if we were descending into old hell, or a nuclear reactor, or many other iconic locations.
My own minor gripe aside, good job on this!