To begin with, there is an awful lot of comedy in this film that many viewers are not "getting". Of course jet Li's Mask looks like Bruce Lee's Kato - he's supposed to, it's a joke. The guy who has a time-bomb sewn to his heart - outrageous? of course, it's a joke! Some readers will probably ask, if this film is supposed to be so funny, why all the excessive and gory violence? well, for one thing the tolerance for this level of violence is actually different, from culture to culture; and while Hong Kong audiences would recognize this violence is extreme, it's certainly only slightly more than average for a HK action film.
Also, Black Mask is really the kind of film that takes a genre's conventions and pushes them to extremes, simply because the conventions themselves are wholly unrealistic. After decades of watching people get shot without any noticeable open wounds, many people were horrified to see Bonnie and Clyde and the outlaws of the Wild Bunch spurting blood all over the place. But the fact is, when you're shot with rapid metal projectile, it's almost certain that blood will spurt, especially from an artery.
This film is a Chinese comic book movie. It is true that the Spiderman films never get this gory - but if they were faithful to reality, they would be! Well, despite its comic-book origins, this film is faithful to reality.
The only complaint I have is the flashy, over-stylized filming and editing. If the makers of this film had shot it with an eye to Hollywood-style nostalgia (as, e.g., The Rocketeer, or the recent Sky captain film), I doubt anyone would have found it offensive.
But as it stands, I still had a lotta fun watching this movie.