As many others have said, you just have to make it past the first few volumes. The beginning is indeed kind of slow, and there's nothing interesting to grab out at you, besides women carrying huge swords slaying beasts. The art is different too, compared to your standard manga style, and it's sometimes hard to tell apart who is who. But other than that, I think it's quite unique and kinda pretty.
As for the story and characters, I find that they're quite beautifully drawn out. Sure, the characters aren't the best, but I think that's what makes them more realistic, even if Claymores aren't human. I mean, if you're looking for characters with insanely strong and unbeatable powers right off the bat, then I don't think this is for you. Each character grows with time, and slowly improves themselves. They're also not all good nor all bad. To me, it gives a feeling of how human the characters are, always seeking to improve themselves, developing with time, and following their own desires. And realistically there's also death, and just not everyone miraculously survives.
Perhaps it's not the greatest, but I thoroughly enjoy reading it. Though I'm certain that not everyone will like this series, I highly suggest you try this series if you have the free time, and are into mangas of this genre, because the summaries and comments don't do it justice; you just have to read it to see for yourself whether it's good or not.