Luc Besson is a master director, with some classic films under his belt. However he does sometimes have difficulty building characters, and giving them the depth the audience might want. This proves to be the case in Joan of Arc. The film really doesn't allow us the insight which many of us really wanted to see.
That said, the film has a lot of excellent qualities. On the practical side, the directing is superb - as is the costume/set design and the cinematography. The supporting performances are wonderful, especially Hoffman's as the Grand Inquisitor, and Jovovich once again proves she has more acting talent in her thumb than most of the world's supermodels.
If you are looking for a movie full of (rather bloodthirsty) horseback battle scenes, along with some political double-dealing and a lot of heroism, then come along and enjoy. If you are looking for a real insight into the mind of one of history's greatest leaders, then you should look somewhere else.
By the way - in case you weren't aware, this story is based on historical facts. I thought I should point that out after discovering that some American test audiences wrote on their feedback cards "Why does she have to die in the end?".