I feel like this movie was slated for Nicolas Cage, and somehow someone decided Vin Diesel should do it to break into a different genre. Basically, the plot seems to boil down to evil witches plotting to unleash a plague, and Vin swashbuckles his way in to save the day, swords and all.
It looks epic, nonetheless — YAY CGI — and has a supporting cast that includes Michael Caine (!!), Elijah Wood and Rose Leslie.