Because, seriously, because of the magnificence of the source material, that movie didn't deserve to suck as much as it did (And also deserved to be like two or three movies).
MAIN PLAYERS:
Wilhelmina Murray: Mia Sara (I'm biased)
Allan Quartermain: Sir Ian McKellen
Hawley Griffin (The Invisible Man): Jack Davenport
Dr. Henry Jekyll: Michael Palin
Edward Hyde: Probably just a CG model with possibly a gruff cockney(?) voiceover by Michael Palin
Captain Nemo: Not knowing very many Indian actors who fit Nemo's profile, I googled until I found Amitabh Bachchan. I don't know if he even speaks English, but he looks cool.
SUPPORTING CAST:
Campion Bond: Oliver Platt kind of seems like the obvious choice.
Dr. Moreau: François Berléand
And then various other characters, like Mycroft Holmes, James Moriarty, The Doctor (Fu Manchu), William Samson, Sr., etc. who I haven't bothered with yet.
Adult Tom Sawyer: Should GFTO.
Screenplay by: Alan Moore, obviously.
Directed by: Christopher Nolan