An otome game, in the most simplistic way I can think to describe it, is a reverse harem. There was a hint of this to Persona 3 Portable from the female protagonist's perspective, as well as in western RPGs such as Dragon Age, but there's very little of that available here.
But this game isn't only about romance. Because it's about the Shinsengumi, there's quite a bit of violence (a part of the reason why the game is rated M).
Chizuru Yukimura is the protagonist. In her quest to find her father, she'll meet many attractive samurai vying for her attention. With a game that blends action with romance, and caters toward a female market, Aksys can count me in on this game. But I don't think men should shy away from playing this either. As someone who's romanced plenty of fictional women in games, it's a different, and still enjoyable, experience. More often than not, it's just hilarious.
Hakuoki: Demon of the Fleeting Blossom releases in NA for the PSP on February 14. I know I wouldn't mind getting this for Valentine's Day...
(In reality, I hate paying for shipping to the UK, so I'll wait until I'm back home to play this. And believe me when I say that I WILL buy this game.)