To fully appreciate the movie, you had to either read the manga or watched the anime or else you'll be lost in all that blood bath. (they did change certain things, e.g. the Swastika on the back of Manji's clothes [to avoid people mistaking it as the Nazi symbol], the time when he became immortal and Rin's background story) Some said KimuTaku didn't age well but imo, but his appearance in the movie suits it perfectly. Manji is an immortal, he looks ragged due to the things he has to do all the time (fight and kill evil men) Manji's not that young (he was made into an immortal at age 26), so you don't expect a young, baby face actor to act as Manji, you won't expect someone to be all clean and proper either when you've been living alone in a small hut in that age and era. KimuTaku is perfect for the role.
For those curious about the kessen-chu (sacred bloodworms), the mangaka left it as vague as possible. He never explained where they came from and how the old woman, Yaobikuni got them.