If your looking for new monsters look no further. Back in the day I spent at a minimum over 500 dollars on books full of new monsters and the 3 creature collection books were far and away the best resource for new monsters. Unlike the monster manuals which were just pictures and stat blocks every monster in the creature collection had long descriptions giving the history, sociology, personality, combat style and adventure ideas for the monsters.
The book does have one flaw that would make me give it 4 1/2 stars if 1/2 stars were allowed. The editor did not do a good job of coordinating between the different authors so there are a lot of monsters that are too similar to each other:
-3 or 4 different types of monstrous humanoid apes
-2 different types of good aligned ravens
-2 different types of magical goats
-2 different types of ghost children
-2 different types of small animals that steal shiny objects from desert travelers
Even with the duplicates you are not going to find a better monster resource.