After reading the first few volumes, I thought this manga was terrible and dropped it from my reading list. Fortunately, I came back, because it gets pretty enjoyable as you progress further and further. The character designs and costume designs are very attractive and the action is fast-paced. While the story is pretty minimal, the stuff that is there is interesting enough to make you want to read more and more. After spending weeks forcing myself through the first four volumes, I read the remaining eight in two sittings.
It does have some fairly big flaws, though. The art frequently gets repetitive since all the Claymores look almost the same, other than slight hairstyle variations, and mostly wear identical armor. It can be troublesome to figure out who is who at times. A lot of the enemies, too, end up looking pretty similar, if not downright identical. The mangaka can clearly draw great looking characters and enemies, but it needs more imagination and variety. I realize it's a shounen manga, but I wish they would spend less time talking about the rankings of the Claymores' power levels. The world is also starting to feel like an all-female version of Berserk.
Really, the biggest flaw that keeps my score from being higher is that none of the characters are really all that likable. They play their roles in the story well enough, but there isn't a single character I'd be upset to see killed off.
Anyway, if you like dark action manga, such as Berserk, you should probably give this manga a try, but be prepared to think the first three volumes are garbage.