As excellent as ever
This is a great game, as I've come to expect from you.
Of course, some of the requirements are just way out there (I never expected to have to play Snake in order to open a door), but that's not a bad thing. Thankfully, you have a walkthrough button for people like myself (i.e. people who are too stupid to figure out all of the puzzles).
And, one last detail: I'm not sure, but I don't recall ever hearing about any Touhou games that use that switch mechanism (unless that's a new feature in Double Spoiler or Ten Desires), so level 15 (and the little bit of the FML mode I tried) reminded me more of Ikaruga than Touhou. But, the name is still deserved, as those areas are at least as hard as I expect most Touhou games to be).
Keep up the good work, and hopefully we'll be seeing "This is the Only Level 4" sometime within the next year or two!