Another is a mystery-horror anime series. It came up when I was browsing recommendations for mystery series, and though horror isn't really my thing, it looked interesting enough to try.
From a mystery standpoint, I thought Another was fairly well done. Once you start from the premise that there's truly something linking the class and the deaths, the way the story plays out is fairly logical. It's got plenty of twists, which for the most part weren't telegraphed too obviously. There's no random plot devices added without explanation, and new discoveries make sense in the context of the world. The last couple of episodes have a decent amount of action (much of it gory) and wrap up the story nicely. We never get a full explanation of exactly how the calamity works, but that's to be expected...it's supposed to be supernatural and mysterious.
As for the horror aspect, I felt that Another under-delivered. I admit that I tend not to allow myself to get sucked into really creepy stuff for the most part, because I'm not a big fan of being scared. (Weird, right?) But in this case, I think even a serious horror fan would have had a hard time getting immersed in the fright factor. In the first few episodes, the director uses a lot of the standard "set up a scare" tricks (creepy music, pictures of weird dolls, long significant pauses in conversations) without there being anything really frightening happening. Some parts are almost laughable...those set-up tricks are used in scenes where Koichi is doing or talking about completely mundane things. Add to that the use of over-the-top blood-spatter-everywhere visuals when someone dies on-screen, and the early episodes seem almost like a parody. This does improve as the series goes on; by the big wrap-up in the last two episodes, there was definitely some tension. It still suffers from the way things were done in the early portion of the series, though.
Another is a nice mystery story, and at only 12 episodes it's short enough that you won't be in suspense for long. Just don't watch it for the horror aspect.