Being 3D instantly makes this game stand out, and it also showcases a good grasp on controls and challenge. Good variety of enemies, and some fun little level-design puzzle bits. The Wriggle segment and entering the SDM stood out especially. I also liked the Hedge Maze area, what with its MASSIVE GATLING GUNS and MOTORBIKES. Reimu's shield ability was nice as well, though I think it'd be extra cool if the shield damaged enemies when touching them.
Fun writing, especially with that somewhat memey dialogue for the final boss. The simple visuals aren't super appealing to me personally, but I won't hold that against the game-- it works for what it tries to homage.
That said, many aesthetic parts of this game felt kinda... flat. Some parts add to an atmosphere, like the lack of music for most of it. But the attacks could've used a bit more weight, for both the player and enemies-- even just a sound effect for the gohei slap would've gone a long way. And in general, I feel some of the less eventful areas of the game could be shrunk down, so walking through them takes a bit less time.
In short, 'twas very good in most areas, but lacked a bit of punch.