Starsinger,
I saw Wicked, I liked it, I listen to the music occasionally etc. I understand Elphaba is not an easy role vocally for most people and is definitly an appealing one for a large majority of the female persuasion.
However, I really don't think it has big shoes to fill. Sure Menzel did a fine job, but it is really a role that anyone with the chops can play. Now I will say the same thing about Valjean, The Phantom etc etc.
However, when you take on the role of some of them mentioned, not only is it exciting but daunting. For example: You are playing Jesus Christ. The show doesn't matter, not even the context, but you are Jesus Christ and this is the role of one of the most influential men in history. How do you do it? It's almost frightening.
For Hamlet. You now have to take on the greatest literary role in English history (and anyone who wants to debate that is free to put on the boxing gloves

The role is so open to interpretation that I honestly believe it is impossible to play it right.
So while I absolutely respect your opinion and agree it's a great female role, I poilitely disagree in it being equal to Christ, Hamlet and Brando (three people I thought I would never compare!)