Claymore's hook is the presence of blonde, nubile young ladies with the titular, impossibly large swords set in a fantastical, medieval world. Being able to move past this premise is the first of many things that this series manages to do well, unfortunately it is marred by a plethora of other niggling problems which turn what could have been a great series into one that, overall, is lamentably mediocre.
Claymore goes wrong by being indecisive as to what it is trying to be and what it is trying to convey. The lithe girls with swords bait is more or less ignored from the outset with a surprising lack of fan-service and obvious lesbian undertones; this creates a problem with what is essentially a shounen series. The "monster of the week" cliché is dispatched with swiftly and a story unravels which thrusts the protagonist, Clare, from one hopeless battle to the next. Neither the story nor the characters are enough to carry this off, its one saving grace is the speed at which the story moves. Not so much adapted, but lifted straight from the manga, the series works on a "one episode, one chapter" progression which means otherwise tedious story elements and swiftly dealt with and otherwise enjoyable combat set-pieces drag on far too long.
The core concept of the Claymores is never investigated, the juxtaposition of human and demon ("Yoma") is only explored within the wish to remain human rather than become a demon. The only obvious avenue taken, the comparison of human activity to demonic activity, is ham-fisted and is overshadowed by the fall from grace of one of the protagonists. Perhaps more poignantly is the (unannounced) flashback of Clare, which gives some measure of emotion with Teresa's pseudo-adoption of the young Clare; again, this is muddied with other threads of genetic memory and paternal instinct rather than fully examined.
The final section of the series is the most obvious target for criticism and is where Claymore collapses under its own weight. Putting more than twenty slim, blonde females into a dark and snowy mountain town probably sounded a lot better on paper; the differentiation between characters though is problematic even with different hair styles and vaguely Germanic runes distinguishing them, battles become muddled and difficult to follow especially after the series has proven that it is not afraid to kill-off major characters.
With all that said, the series does a lot things which set it apart from other, similar medieval styled anime. The obvious comparison is to the seminal Berserk and although the first episode is brutally similar in both tone and character, Claymore manages to distinguish itself by providing a healthy set of spectacular revelations as well as being almost consistently aesthetically gorgeous. The carbon-copy Claymores are offset by universally excellent monster design, the cannon-fodder pawns giving way to gargantuan and ornate entities, rippling with spikes, blades and wings. Its grounding in reality is a big selling point, despite the presence of deity-like demons and sword-wielding witches, it feels very substantial and tactile and never explains things away through magic, opting for a more identifiable spirit or "Yoki", to use their parlance.
It's very easy to pick fault with Claymore, the final fight with the angelic Priscilla an obvious bone of contention for fans of the manga; while the whole may not be more than the sum of its parts, the parts themselves stand well on their own and the series only begins to drag towards the finale, otherwise it is an enjoyable, blood-filled romp through just another hellish world.