The visual novel is really fantastic, though fairly slow-moving if you're not used to the medium. (Visual novels in general tend to be very detailed and very slow-paced. Some, like Higurashi, use this to great effect, but it can also annoy people not used to them.)

If you're not sure about reading it, the anime is also really good. It's obviously much less detailed than the visual novel (compressing ~40 hours of visual novel into TV format is hard) and omits some sizable plot points, but it's still great. The first half is fairly slow set up before it hits like a truck.