A very interestlying done visual tone poem with a somewhat baffling ending. Not baffling in that I didn't understand it, but baffling in I didn't understand the filmakers choice to completely expunge the denouement of the original tale. Instead of delivering the final chapter of the tale, where the lord that Gwain is staying with is in fact the green knight, and that Gwain survives the encounter to return home, it's left open ended...which leaves the moral of the tale to be lost.
Yes, Gwain finds his courage and faces his death, upholding his honor and the honor of his organization (after a "Last Temptation of Christ" cutaway), but without familiarity with the original source material the ending is needlessly ambigious.
Perhaps it's that way to encourage people to find the tale, or tell it on their own, but it does leave a bit of a tarnish on what is otherwise an excellent and haunting film.