SPOILER ALERT: Because of a prophecy that a king will rise from the Cimmerians, the bad guys wipe out the entire Cimmerian people, leaving Conan as the sole surviving Cimmerian to track down the killers one by one for revenge. So its basically Kill Bill meets the Massacre of the Innocents.
Needless to say, this bears no resemblance to anything Robert E. Howard wrote; in the books Conan is happy to take revenge here and there for various things, but his main story arc is not one of revenge; and since Howards Cimmerians are supposed to be the ancestors of the historical Cimmerians, it makes no sense for them all to be wiped out.
In any case, the archetypal Conan image is not of the hero clanging his sword down on some fellow thugs head as these screenwriters seem to think; its of the hero sneaking into an ancient, mysterious, exotic, ruined, vine-covered, demon-haunted temple to rob it. The whole lush atmosphere of Howards stories the shining kingdoms … spread across the world like blue mantles beneath the stars … Zamora with its dark-haired women and towers of spider-haunted mystery … Stygia with its shadow-guarded tombs, Hyrkania whose riders wore steel and silk and gold … and Aquilonia, reigning supreme in the dreaming west has never come close to being captured in any movie version (whether for budgetary reasons, lack of imagination, or both), and this new script promises no improvement.
The reviewer also expresses disdain for the comic-book versions of Conan; but actually most of those have been pretty good (the high points being Marvels 1970s series Savage Sword of Conan and the recent Dark Horse series), and far more faithful to the original than this forthcoming mish-mash.