This has been an excellent expansion to the wonderful system. I've been playing a very simple version of Hero Kids (using their cut out figures, characters, maps, adventures etc.) with my 3 year old son. He loves it!. With the new monsters, the adventures have become even more fun and interesting for him as there's a new monster that shows up each adventure. His curiosity is piqued and play stops for a minute as he looks long and hard at the artwork on the cut-out figure. He then starts asking questions: What's this called? Is this a bad guy? He looks scary, will he get me? Can I get him first? etc.
After becoming familiar with rats, skeletons, bats, phantoms, pirates and the other monsters in the base set, this new set has been a lot of fun to introduce.