having seen the show first and read the book second (which puts me in the minority, i know) i think most of the characterization works like a standard musical, so it's accessible. Nessa and Boq need a bit more, but i did follow the Fiyero/Elphaba/Galinda triangle fine as a first time viewer.
Structure-wise, what i'd do is take out the "Chenowith specialty" at the beginning. For me, the show didn't really kick into gear until the flashback started. it sounded pretty, the Chenowith high notes were thrilling, but you couldn't catch a lyric. And i'm used to Sondheim lyrics, so i'm not slow at them. Traditional song format from operetta on is for the melody to be stated in a register where the ear can follow it, and then it might be repeated by a chorus while the obligato for the soprano ornaments on top. In WICKED, it starts out with so much ornamentation, and the chord structure is atonal so it sounds "modern", and the result is a mix which can be confusing and uninviting for a first time listener.
Modern musicals are notoriously hard to start, to get an engine going for the evening. i wish i had a solution for how to introduce a conventional audience to WICKED as a musical, but i don't---i'm just saying what i saw didn't seem that effective to me.
Will: They don't give out awards for helping people be gay... unless you count the Tonys.
"I guarantee that we'll have tough
times. I guarantee that at some point
one or both of us will want to get out.
But I also guarantee that if I don't
ask you to be mine, I'll regret it for
the rest of my life..."