I love werewolves, but there are honestly very few werewolf movies I like. An American Werewolf in London, The Wolf Man, and The Howling are very much the best, and even those didn't really get it 100% perfect. I think both Ginger Snaps and Wolf (Jack Nickolson) started out pretty good but quickly nosedived and never recovered. Brotherhood of the Wolf was a great, great movie, but wasn't really a werewolf movie per se.
So what does a good werewolf movie need?
Special effects? Yeah, they matter, but it doesn't make the movie. An American Werewolf in London had a great transformation scene, but after that, you could tell it was a muppet. A scary muppet, yes, but a muppet nonetheless. And The Wolf Man? Great effects for its era maybe, but it definitely shows its age and the limited technology of the time. The Howling had really good effects, but that wasn't what made the movie for me.
To me, the central aspect of the werewolf is transformation itself, that play wherein we examine our struggle against the bestial nature. Or better yet, the embrace of it. And all three of the best werewolf films (see above) did this spectactularly. Ginger Snaps and Wolf tried, but ultimately their writers didn't seem to know what to do with the werewolf once they got it there.
But the best werewolf movies are those in which the characters struggle with "the beast within."
Someone already mentioned Jekyll & Hyde. Good call. I agree 100%. I'll add another: Marvel Comic's HULK, wherein weak but brilliant Bruce Banner struggles against the raving brute inside him.
Brotherhood of the Wolf. Great movie no doubt. It starts out teasing you with a werewolf theme, but then turns out not to be. Or does it? Remember that the best werewolf stories deal with that story of the beast within, and one of Brotherhood of the Wolf's heroes is Mani, the Native American, whose guardian spirit is the wolf. But because he comes from a culture wherein the wolf is honored and even venerated, his embracing the wolf nature grants him a nobility and fighting prowess that is lost on the European characters in the film.
But in Brotherhood of the Wolf, the theme of transformation is carried even further. His friend Gregoire de Fronsac is a libertine, a man whose greatest weapon is his mind. He lets Mani do all the fighting. Until Mani dies, that is, and then Gregoire seems to embrace Mani's wolf nature, and he single-handedly massacres Mani's killers. It is very much a transformation.
And I'll give you one more. It isn't a werewolf movie, per se, but still very much concerned with the theme of transformation and shape-shifting: The Secret of Roan Inish. One of my favorite movies, and it deals with the transformation of its characters: One branch of the family who are ordinary humans, one branch of the family who are shape-shifting selkies, and the so-called "dark ones" who walk the line between. It's a great, great movie. If you haven't seen it, check it out!