A bit late to the party but here's my 2cents about this demo:
Gameplay: Kinda broken and unpolished tbh... but then again, ZUN has to balance not only the release gimmick, but also 16 shots. Its no wonder some of these things are a little overpowered... however if you don't use Releases (Which is how I plan to play the full version, in the case ZUN cant fix the broken Release thing), it actually plays decently and its kinda fun. Not Best Touhou game material, not even close, but it will hopefully turn decent-tier at least (So long as its at least a slightly better than TD I can get into it). Stage portions are kinda meh, ESPECIALLY Stage 2, it looks a lot like LoLK?s stage 2 and its also boring af.
Music: Ehh... its kinda there. Not much of a fan of this game's ost so far, sorry. Only 2 themes I actually really like are Nemuno?s theme and Stage 3 theme. Everything else is honestly kinda forgettable so far.
Best Newcomer/Bossfight: Nemuno, because her theme is among the best so far, I like her design, and is basically pretty cool for a Stage 2 boss... Don't particularly care about the other 2 bosses so far. That said, her nons are stupidly bland. I hope ZUN changes those nons in the final version, even though we all know that most likely ZUN wont change/will barely change the base game as it is now...
Overall... I think it will turn out to be a decent game. However if I am being honest, I expected a bit more from it. Then again, might be a bit unfair to it, because it has to compete with LoLK?s demo (Regardless of how the final game turned out, when LoLK?s demo came out, I was HOOKED to it. I really, really wanted the full version to come out to try the new stages!... Not getting quite the same feeling of urgency with this game?s demo).