Hyakki Castle sets classic party-based dungeon crawling in an Edo period castle, pitting character classes such as Samurai and Ninja against "vivid monsters and supernatural creatures from Japanese literature." Based on the trailer above, I think it's fair to identify it as something like a Japanese Legend of Grimrock—that being the best and most recent first-person dungeon crawling series I can think of.
Outside of the theme, the most fundamental difference in Hyakki, at least as far as we can see from the trailer, is that your party can be split into two groups (2-2 or 3-1) and sent off to do different things, or attack enemies from different positions. "For instance, one character can lure a monster while the other three lay in wait for an ambush," reads the press release, "or the party can split to flank a monster or to solve a puzzle."
Party splitting is a novel idea, and I'm excited to see what sort of puzzles the system makes possible, though I do wonder how the complexity will pair with a genre already steeped in it. Developer Asakusa Studios—which is based in Asakusa, Japan, naturally—and publisher Happinet are bringing Hyakki Castle to Steam this winter, so we'll be able to give it a go in short order.