The second volume in Gregory Maguire's Wicked Years series is Son of a Witch, which picks up where Wicked left off and follows the continuing exploits of the residents of Oz, including Glinda, Liir (the eponymous son of Elphaba, the Wicked Witch of the West), the Scarecrow, and others.
I enjoyed Son of a Witch slightly more than I did Wicked, but like the earlier book it's not one I'll feel compelled to read again. Maguire tries diligently to build up his characters, but most of them fall completely flat. Far too much of this book seems to be spent having characters wander around Oz willy-nilly (making the map at the front a very necessary thing).
I'll read A Lion Among Men (the third volume, just out), but I'm going to keep my expectations low.