Perfect for mixing things up in your campaign. Its a nice variation of the typical goblin encounter when your throw brand new encounters with unique monsters that will throws your players off a bit. The book also has an appendix for treasure and experience for most of the prominent retro-clones like OSRIC, Sword & Wizardry, & Labyrinth Lord.
The book is very solid and I highly recommend grabbing a copy. You can buy the print version through Lulu or the pdf from Drivethrurpg.
Below are my top five creature from the Creature Compendium. They are not in any particular order but showcase some of the creativity infused in this book.
Fetch: A spirit creature that lives inside a mirror. Adventurers passing by must save vs paralysis or be reduced to a catatonic state. Then the Fetch jumps out of the mirror to assume a doppleganger form of the victim. It then proceeds to slay its victim.
Gaseous Lanterns: Flesh ballons with tentacles.These ballons explode with contact with open flame or if attacked by an edged weapon. When they explode they release toxic gases plus they cause a chain reaction of explosions if other Gaseous Lanterns are nearby. Perfect for creating a cavern with dozens of these creature and making the adventurers cross this mine field.
Kam Warriors: These 4HD supernatural warriors rise from being slain. When this 4HD warrior is slain it rises as two 2HD warriors. When the 2HD versions are slain they spring up as two 1HD creatures. Very cool ability.
Flash Dragon: Giant Lizards with the ability to teleport around the battlefield. They teleport to create flanking positions.
Once again I highly recommend grabbing a copy of the Creature Compendium!