Let's see. First of all, I'd like to start with my memories including shmups. I always liked them, but my childhood was mainly about one game: Tyrian. I just loved its music, its gameplay, and most importantly, the fact that it's a very long story with a detailed world. After this game, I never ever found a shmup similar to that, they were all short with no story at all. Until I found Touhou. So why I like Touhou?
1. The setting.
I just love the whole setting of the game. I was always fascinated by Japanese myths, but this is the best interpretation I have ever seen. Also, I like how everything fits together into one, slow, idillic place. Some people usually hear me saying that today's world is wrong, because I feel it is wrong, and I feel Gensokyo to be completely right. I just love how everything sounds childish and not at the same time. I love the ideals of this world setting, and the ideas about maintaining the utopian setting. I also like that things, what aren't normal, or go against Common Sense are totally normal in this world. Also flying. Damn, I'd like to do that, ever since I was able to fly naturally in my dreams. Who knows, maybe my dreams take place in a Gensokyo-like place without me realizing it? It is truly a wonderland.
2. The stories
Yeah, I like the laid back stories. I like that they are not really that serious. I like that they could be even stories for little kids. I just love them, and I love the canonical stories too, especially the ones about the Three Fairies.
My only problem is that they are too short. This is the only thing I don't like in Touhou games, that there are only 6-7 stages.
3. The characters
They are all a lovable bunch, and I like them despite them being cute and such. It's not a lustful thing to me, they are just plain awesome and real personalities. I also like how their personalities aren't said aloud in dialogues, but shown in the form of their danmaku and theme music.
4. The Music
When I was little, my mother was very concerned about the fact that I never liked music, only the music of movies and mainly, the music of video games. When I found out about Japanese Music, it fascinated me, and I thought "It's just like video game music, only with lyrics!" And when I found Touhou, I was blown away. It is video game music, and very good video game music, considering how the soundtracks of today's video games are all lacking. And thanks to the fans, it can be really a "video game music with lyrics".
5. The gameplay
I still say this: This is the most fairest game of all time. No fake difficulty, no tricks, no rules to put you into disadvantage, only rules to help you. When you suck at it, it's your fault, not the game who wants to fail you. The best kind of game.
6. The Danmaku
Ho boy. They are beautiful. And the fact that they basically tell us the personality of the characters to fight with, it's awesome. I mean, I can't really like a character in Touhou 'till I fought with them. Why would I like her, if I don't even Know her? It was the case with Koishi: I never liked her, I never knew her, so I couldn't like her, because how much time it took me to even 1cc SA Normal. But when I finally did, and I could fight with her (even though I haven't defeated her yet), now I know her much better, and I started to like her. This is the language of Danmaku, what makes people to know each other.
The only thing I don't like is most of the Fanon material in the story department is usually either silly, stupid, goes against canon or all of them. I am a person who likes the Canon of Touhou, and I don't really like the kind of Fanon that goes against that. But I like those Fanon ideas very much what can go well with the Canon.
Oh yeah, ZUN is an awesome fellow, I think I can understand him very well.