First Knight isn't faithful at all to the story of Arthur and the costumes, lighting, and settings were all terribly modern, but the story itself was well done enough that the movie makes up for the rest of it.
It follows the story of Arthur, Guinevere, and Lancelot and thier journey from the time Quinevere and Lancelot meet by chance as her carraige is ambushed on her way to marry Arthur, through some more kidnappings, a wedding, and a knighthood, to the death of Arthur. Lancelot, who begins as a mercenary, grows a great deal as a character, while Guinevere's struggle to control her feelings for him is painfully clear. Sean Connery's Arthur is the kind of king one would expect of Arthur, kind, understanding, with a rigid set of morals that he cannot break even for his queen. Julia Ormond makes it clear that Guinevere loves both men and Richard Gere's sensitive performance and longing looks tug the heartstrings.
In essense, it is the acting and the love story that make this movie enjoyable. It is a remarkably un-historically accurate movie and there is not much in common, aside from the names, with the traditional Arthur legends, but these old stories are made to be interpreted. The romance of the movie is what makes it worth watching...that a Richard Gere looks really, really good.