I haven't been able to buy Touhou 18 yet due to irl stuff (though it should get taken care of tomorow), but I just couldn't wait, and I watched BeatMario play Touhou 18. And while I haven't listened to the tracks too much for now (I'll correct that while playing), I do have things to say for the designs.
First of all, for the demo characters, Mike and Sannyio both have an amazing design and themes too. Like really, ZUN outdid himself for them, they're both top tiers designs and themes for stage 1 and 3. Takane is also great, especialy since she's a new kappa, though her theme isn't nearly as good as Mike's or Sannyo.
Now, for the spoilers.
Misumaru's design is a point of contest, but I personaly like it a lot, i just like how otherwordly it is. It is a bit weird tho, but I like it. I will say, the fact that she made Reimu's yin yang orb is pretty mindblowing, since that's really big. Also making magatama is cool. The stage she's found in being named "Izanagi's Factory" is somehting that could imply that Izanagi is linked to the Hakurei God, which is also pretty big, considering that Izanagi created Japan in his myth.
Next, Blue Aya, or Megumu. I love her deisgn, it's awesome. Like really, it feels like she's greater than Aya hierachirchaly, while still being kinda like her. And she quite literaly made the accident to gain profit, she's so awesome. She has one of my favorite design, though not quite on the same tier as Yacchie for me, who I really loved from the begining, though I still apreciate her a lot.
Following that, Tsukasa. I also like her design a lot, it's simple but really effective. Not too much to say here, but she seems like a fun character.
Now, the final boss, Chimata. Boy, now that's an overdesigned character design done right, she's what most people would think when thinking of a Kingdom Hearts character based on the rainbow, and I love it. Also her cape is the sky, and that's super cool. Also, her power is like Shion and Jo'on's power combined but that cannot be used for her own profit and far stronger from what I get, and that's kinda awesome. She also calls the heroines robbers aparently, which is very funny but also very accurate to how Reimu, Marisa, Sakuya, and Sanae can be.
And finaly, Momoyo, who's design is beyond genius. I love it. I love every part of it. It's even better than blue Aya. ZUN definitively outdid himself in a way no one ever expected him to do so with her. She's also a dragon slayer and can aprently eat dragons, so that's cool. I really like her a lot, and the fact that the game goes "yeah, that's a giant centipede that eats dragons", which only makes her design that looks like she's from a minecraft anime adaptation only makes her greater.
In short, I love those designs, even the controversial ones, and the new characters all seem like they're awesome addition to the lore.