Claymore has a very interesting plot, and the voice acting and animation are nice. Superb use of character development is a major aspect of what makes this anime so good. It was suspenseful, and there were many times when I couldn't wait to find out what happened next, so I ended up watched several episodes in one night.
It has a mixed ended, with some closure but also intentionally left open, which makes me wish there was a second season. I suppose I'll have to pick up the manga to discover how the story continues.