I was curious and I played a bit. So, I'll try to give you some feedback.
I will not comment the graphical part (it's already enought impressive that you make all by your own alone) but I think it lacks a bit of animations. Especially on menus and for the bosses moves.
Players are nice but I played with Sanae A and i found her shot really weak. I try a bit Reimu A (on Ura) too and... same thing. It take an eternity to kill Cirno. And Marisa A stars are near to invisible. But aside that, players are cools. And I like ReimuA's shot type.
About the menus:
-When you're on a sub menu and go back on the main title menu, the cursor go on "Quit" instead of the previous choice. It's not a bug but it can be really annoying.
About the stages (I try it on normal and just a little try on Ura but I died on Reisen's first nonspell).
Nothing to say on stage 1. Just, Cirno have to many life and her nonspell is not really exciting. But aside that, it's decent for a stage 1.
Stage2:
Well, I know I say I don't speak about graphics but... thoses gray lines are... what is it in fact? It's just disturbing and ruins the background.
For the Sun effect on Flame Sign "Glowing Sun", just avoid Laser for the sun. The animation for it's spawn is... not good. Really. Insted, you may use just a bullet with ADD blend and then change his scale. If you don't know, you can use all( or almost all) the ObjRender function on a bullet object (since it also have a render).
It's just a delait and don't change the spell but small details like that are really important to get a good looking game.
And the spell was a bit hard with really low bullets.
And Same thing as Badz for the curvy laser. They are deadly and it's hrd to deal with. It's espacially true with all danmakufu curvy lasers.
Stage 3:
The first red vortex is hard to get with all these lasers and aimed bullets. But if it will be used well, it can be a good place for it. Maybe you should couple it with a blue vortex. More risk, more reward.
The stage itself was not bad. But I don't found it less memorable as the second one.
On the other hand, the boss is really cool and I enjoyed the fight. There is just two issues:
The kodama curvy lasers cause lags and the last spell is too longwith SanaeA. It take an eternity and become boring. But I like the spell. I do it with Reimu and it was far better.
Also, two other issues:
The life and bomb parts are too dark and it's hardto see them behing the bullets. And some of the musics names pass under the gauge thing on the right. It's the case of Sayuri's theme name.
Well. It was nice and good luck to finish it ^^