I usually prefer boss themes significantly more than stage themes, but this time I love them both equally. ZUN's new music style is quite different, and I welcome the change.

Not saying his previous style was bad, of course. It's just nice to hear some variety. I was also pleasantly surprised by the two songs he did for Hopeless Masquerade, which I almost didn't think were done by ZUN until I checked the music room.
As for gameplay, I'm pretty satisfied. 1cc'd on Hard, and it was a sufficient challenge for me, and the gimmicks for each boss were quite interesting. Sekibanki's my favorite so far in terms of design and danmaku. And those heads are just adorable. :3
I couldn't be more excited for the full game to come out. So far it looks very promising to me!