“King Arthur: Excalibur Rising” (*1/2 out of four) was a less-than-exceptional retelling of the Arthurian legend about Arthur’s illegitimate son Owain (Adam Byard) who must realize his destiny and take up his mantle as King. Reasonably compelling at first but it soon sputters to a halt and becomes talky and sluggish. Muddy cinematography and cheap-looking sets aren’t much help. Yet another film obviously inspired by “Braveheart” and also “Robin Hood” but fails to match the sparks of either.