My three favorite returning monsters are
1. Linnorms - Loved them in Dragon magazine. I hope they have pictures for each one.
2. Zodar - A mysterious humanoid found in the back of the 2E Spelljammer compendium returns! IIRC, these guys were tough as hell!
3. Spell Weaver - just plain cool...
Some of the newer monsters I can't wait to see are: Hellfire Wyrm, Ethereal Slayer, Bronze Serpent, and Ocean Strider. The new monsters (Tojinada?) in the MM1 pale in comparison.
The Morkoth, Death Knight and Frost Salamander are well drawn as well. I'm hoping this book has a better layout than the MM1.
On the flipside, I can do without Gem Dragons and Ixitxachitl. Dire elk? Half-golems? Not sure about those ones...
It still looks much better than I expected. I was cynical about buying another MM, but now I definately will get this one.