Very fun! I enjoyed every last bit of the game to the point I No-Missed it - it wasn't too hard mostly thanks to the I-frame mechanic but still.
Only thing that's missing is the boss marker, this thing at the bottom of the screen that's here to indicates where the boss is - but it's not an issue, just quality of life.
It's probably obvious and already said but I think it too: it's really great to see the pattern fusions and all the tag-team things! The danmaku patterns are also recognisable for each boss character, which is pretty great fanservice for a Touhou player like me! The theme mashups too, they're as great to listen to!