After looking through the Monsters of Myth PDF again, I had to smile a bit and even simply shook my head at some entries.
Overall, it's an interesting book. Many of the monsters are just plain silly in my opinion. Some stretch the imagination just a tad too far. A few are actually pretty good.
One of the monsters I found in it that I liked a lot were the "Jotun" Giants. I like my Norse mythology and recognized the giants of Jotunheim right away. There's even a possibility I might find a way to use them in a future adventure or two.
All in all, I give the Monster's of Myth a C+. There a fewer "serious" monsters in there to make it really useful in my one person's opinion.
Having said that, it is fun to look through it just to find one of the few real gems that it has to offer. Even a bit more fun to just read some of the sillier entries.