I wouldn't say it's mediocre. The production values are very high, and the direction and mise-en-scene (acknowledging the slight vagueness of the term) are very impressive. It's a good film, one elevated by the extraordinary talents of its director and other collaborators - but you're right that it's a very strange inclusion on the Cahiers list.

Though I suppose this helps make sense of it: <!-- m --><a href="http://www.sensesofcinema.com/2008/cteq/moonfleet/" target="_blank">http://www.sensesofcinema.com/2008/cteq/moonfleet/</a><!-- m -->

Really surprised this is on the Cahiers list... felt like straight mediocrity to me, save for one great scene with a halberd.