Watch this for Jackie Chan's riotous fight choreography. Or for Owen Wilson's shameless goofball acting. But whatever you do, don't expect historical accuracy. The movie is fun to watch, but it doesn't have a serious bone in its body.
To expect otherwise is to set yourself up for disappointment. Chon and Roy go to England to rescue the Chinese imperial seal stolen from Chon's father. They're helped in their quest by Chon's adorable sister (who Roy predictably falls for) and Arthur Conan Doyle (who has somehow become a Scotland Yard inspector, but remember what I said about accuracy). Cool fight sequences ensue.
The DVD has an interesting interview with Chan about the fights. There's also a couple of commentary tracks and the other customary fill.