While MWoO wasn't the greatest Muppet production ever done, it does show promise. While I do have some issues with it, I really think that all things considered they did a good job of "muppetizing" the Wizard of Oz. As this script shows, it is hard to meld a recognizable character with another role, and maintain both characters' integrity. Take Rizzo for instance. Steve has to voice him as Rizzo so we recognize him, but at the same time he has to convince the audience that this is the Munchkin Mayor.
Yes everyone wants their favorite character to get more screen time, and has quibbles about the way the voices sound. However, I think they did an excellent job of packing as many recognizable muppets into the cast as they could, and were very true to the book. (A rarity these days.) There certainly was room for improvement, but I think that this was one of the best Muppet productions in quite a while.
Overall: B-