After reading through the Muppet Wiki...
1 Wondering why 80s Robot wasn't included given his creation and popularity owed to both the new movies, TM and MMW.
2 Surprised Anthony and Fern were included, they're the only ones from JHH. Unless you also count Bean Bunny and Clifford.
3 Points awarded to the MCE for finally listing all "Dr." titled characters together alphabetically correctly... But then I have to take those points away for a couple of inconsistencies like The Mooppets before Miss Mousey when they should have followed Miss Piggy and similarly for Mr. Poodlepants in the P's, but then before the Pigs.
4 Why is a Snowth included with the Koozebanians?
5 Why did Fletcher Bird get a solo entry of his own instead of being lumped with the Birds? Conversely, why didn't Bad Polly/Polly Lobster get his own page?
6 Shouldn't the Toms have been included as Old, Real Old, and Dead Tom instead?
7 With the wealth of obscure characters included, I'm a little disappointed we didn't get at least Irving Bizarre, Vendaface or Vicki, as well as separating all the unnecessary group entries so Yorick could have had a solo page to get as complete an alphabet possible. True, an X entry would have been missing, but I doubt people putting the book together would know about Xomfie and Melg, the Pink and Yellow Stalks from Sex and Violence; and even then, they'd have probably been put together as "The Stalks" or lumped with the "Monsters".
All in all, I give the MCE 4.5 out of 5
With a publication like this, I hope future follow-up editions are made including more characters that got left out of this initial run; and that other branches of the Henson Universe get character encyclopedias of their own.
BTW: I don't believe that inclusion of Sam & Friends or Rufus from Hey, Cinderella! automatically denote Disney ownership of either property unless information surfaces proving such.