I thought I'd hate it.
Awful art, dubious writing, creepy lolicon subtext, no puzzles, and fans who post You Tube
videos of 'Lunatic' runs of impossible difficulty, as if sinking endless hours into a game were something to be proud of. I was not raised on shooters; I am a text adventure person.
But I'd missed the point entirely. The point of Touhou, as far as I can tell, is not to win. There's no reward; nobody will write you a check for all those hours. It isn't to see the ending or follow a coherent plot. The feeling of accomplishment might be there, but it's probably going to be tinged with guilt - don't you have better things to do with your one life on earth?
The point of Touhou is to focus, and achieve moments of absolute, beautiful flow. The point is to develop absolute calm in the face of music and animation designed to throw you off, to make you frenzied and manic. Eventually, you stop seeing the spinning backgrounds and the bullet patterns that distort your motion perception. You stop seeing the bullets at all; eventually, there are only gaps. This happened to me within the space of a week-and-a-half of irregular play.
(Note: I say "irregular play," because there's no way to marathon this game, at least for me. After about forty minutes, it becomes unplayable. Focus just doesn't stay that long. I do best when I pause and do something productive for a while.)
If you are of the mindset that a game is to be BEATEN, and beaten utterly, this ain't the game for you. I'm unlikely to ever see the extra boss (though who knows? I'm getting better). If you take losing personally, or find it frustrating to lose, this game will either turn you off, or break you of that attachment to victory.
You are not there to win. You are there to graze bullets, shoot bombs, admire elegant bullet patterns, and then find gaps in them. When you are doing well at Touhou, you are not playing, but being. Your tiny shrine maiden is an extension of you.
You are the loli.
CONCLUSION: Still creepy, but in a Zen way.