I too, also feel that he's very inconsistent between his scores. I love his Godspell and Pippin scores and I like his lyrics for Hunchback and Enchanted.
Wicked, IMO, is one of his weaker scores. Some of his lyrics are laughable for all the wrong reasons. I felt that the only memorable numbers were What Is This Feeling?, Popular, Defying Gravity (which is remembered more for the flying effect than the song itself),and For Good.
"You drank a charm to kill John Proctor's wife! You drank a charm to kill Goody Proctor!" - Betty Parris to Abigail Williams in Arthur Miller's The Crucible