I'm only reviewing the anime. I haven't read the manga or the original novel.
Plot: Another's plot isn't spectacular. It did had some enjoyable mystery elements and it keeps you guessing. However, by the end there were still some things that weren't explained sufficiently, so they just seemed like lame plot devices.
Visuals: The graphics are pretty and vivid, and the distorted crazy faces aren't absolutely narmy looking (I'm talking to you, Higurashi), which was nice. The color palette is bright and the characters look like they came straight out of a romance anime. Don't be mistaken, though—the gore isn't toned down because of this.
Audio: The voice actors did well. Both the opening and ending themes (ALI PROJECT and Annabel, I think) were enjoyable.
Characterization: The characters are pretty static. Any attempt at character development for Misaki seemed to fall short. I won't complain too much though, because anime was short and its main focus was on the horror element.
Content: Most all of the death scenes are very graphic and gorey. So of course, if you get queasy seeing a girl get impaled through the throat by the sharp end of her umbrella, then this anime isn't for you. There isn't much sexual content until one episode when the camera lingers for more than a few seconds on the girls'...assets.
Overall: I'd give this anime three stars. It was enjoyable to watch simply for the gore and crazy deaths, but not much else.