Classic arcade style shmup fun, crazy shooting and speed action in a short + fun experience.
The dialogue is funny, the graphics are simple and pretty to look at, the gameplay can get fast and crazy, and it's got everything you'd expect from a decent vertical shmup game. The cheesy anime music, big bosses, nothing on screen but bullets of weird shapes and colors. It's all there. The controls are as simple as they have to be and it's easy to get right into and start blasting away at things. The best part? It's in English and it's out in the states. So, if you can't play Mushihime, you'll get your fix with this game.
If you can find this game, it'll be for cheap and you'll have no excuse not to buy it. It's on Gamefly for rent and I recommend that if you can't find it for purchase. However, you might be in better luck buying the third game if it ever comes out for consoles. So far, Shikigami no Shiro 3 is only out in Japan as an arcade. The soundtrack's out though and is quite rocking.
It's hard, as you can imagine, but you can toggle the difficulty to make it easier if you need some help. Now if only Einhander had that option, eh?
If you need a short but fun game to pass some time, look no further than Castle Shikigami 2.