I also appreciated the imagination that the design team put into creating the Mouth. He didn't seem that impressive when I first saw him (in fact I almost laughed at times because it seemed like he was too over-the-top), but once I watched some of the appendixes and listened to what the team was thinking and how they added things here and there and what their reasoning was behind some of his design I was pretty impressed.
Now I can at least watch the scene without stifling laughter, although I still don't appreciate how he meets his end

(but that's a subject for a different thread).