Maybe a bit slow and long for some. I didn't mind the pace. I liked the mystery. I liked the characters. I liked the music. It did have a creepy atmosphere but it could have been amplified at times. The spoilers are where the movie gets good.
MAJOR SPOILERS
Was the girl Lucifer is disguise? She seemed to be judging Corso and even looked pleased when he eventually killed someone. Corso was immoral but I don't think he was evil. In the end when corso and the girl were having sex, I think Corso knew who she was. Lets not forget that the girls floats in mid air, so it was pretty obvious she was at least and angel or something. But In the end Corso gave himself up. He was willing after temptation. He fell in love maybe. And the devil was on his his shoulder the whole time during the movie.
He was already moderately sinful at the beginning, and that was a great start to the character. I liked how Lucifer wasn't interested in stereotypical worshippers or people obsession with her, but wanted to manipulate. The girl or Lucifer is even seen reading How to win friends and influence people in the lobby. After all Corso is the one who approached the girl, who also has the appearance of two faces in a reflection. The devil has two faces remember.
This is a movie to re-watch for sure. I can see why it went over people's heads as it's so subtle and makes the viewer work hard for clues, not that it's an insanely complex plot. But one thing still evades me, and that's why Lucifer wears odd socks? Pure evil

Johnny Depp is near his best in this devilishly demonic detective story. He is an unscrupulous, but knowledgable, New York rare book dealer who is charged by the millionaire Frank Langella to authenticate a text. "The Nine Gates of the Kingdom of Shadows" may or may not be able to summon the devil - or, at least, bestow the owner with some semblance of Satanic power. His search for the truth involves deceit, lust, many murders and a cat and mouse game with deadly consequences. Emmanuelle Seigner is suitably enigmatic as "the girl" - a sort of angelic person with ninja skills and Lena Olin hams it all up nicely as the sex-kitten (with claws) baddie. I enjoyed this; it is a complex supernatural thriller that doesn't try to impress with cheap special effects (though the music can be a little annoying at times); it's well written with a strong cast. At 2½ hours, however, it is too long; there are plenty of establishing shots that could have been trimmed/dumped to up the pace a bit more.

This is a beautiful masterpiece. Mysterious, dark and occult. Everything is great about this movie - the soundtracks, the story, the atmosphere... The sets are Gothic and gloomy, the music is aptly fitting, the acting and scripts even more so; nothing breaks the persistent, unshakable scene and tone that is set by Polanski, who has obviously taken into careful consideration every possible factor to create a deeply immersive, memorable experience for the viewer. There's not a single part in the movie which would bore you. I can't think of a single thing wrong with this movie. I can't find any plot mistakes. Actors are delivering superb acting, especially Johnny Depp & movie is very well directed. This movie is a good example that proves that you don't need a ton of action to make a good thriller. I thoroughly enjoyed it from beginning to end. This movie has so many hidden gems that you need to re-watch over and over to fully grasp the craftsmanship of Polanski's epic movie! And I have seen it more than ten times. That's how great is this movie.