Trick or treat, smell my feet, give me something good to eat! If you don't, I don't care, I'll just change into an actual superhero and beat the candy out of you, you creepy monster!
If you've played the first Costume Quest, then you know exactly what you're in for- kids beating the crud out of monsters for halloween candy. But this time... there's more to it than just "the bad monsters want to steal away our candy". Nope, this time, there's a new villain in town... the one person who has more reason to hate candy than any one other person in the whole city...
...the creepy local dentist.
In fact, he hates it so much that he's somehow managed to make it to where Halloween, candy, and costumes are crimes against his order, and he's recruited the Repugians to help enforce his views. It's up to Wren and Reynold to put a stop to it, and save Halloween for future generations.
To be quite honest, this is just as good as the first one- battles are a tad bit more complicated with a bit of Pokemon-style type weakness mixed in, but you'll pick up on that easily enough. Stickers are also gone, replaced with Creepy Treats cards that recharge after a certain number of battles. The automatic healing after every battle has been removed too- but it's not as terrible as it sounds, honestly. You either need to camp out around a water fountain to keep healed, or finally put that candy to more use than just as a currency- you can fully heal your party for 25 pieces of candy, or use it to buy upgrades and cards.
To be honest, the new costumes you get in this one may not be as powerful as some of the originals- for instance, the Unicorn's My Pretty Panacea special is still brokenly powerful compared to the revive you get without the preorder- but the right combinations are still very, very powerful.
Enemies are no longer a finite resource- there are respawning enemies in all the areas of the game in addition to the ones in the usual places, so if you just feel like sitting somewhere and grinding levels, you can do that, too. To be honest, though, you don't need a super-high level to beat the game- I finished it around level 9, with the Hardcorn achievement, even.
Some of the late-game random encounters need a specific strategy- you'll run into a group that can drop a group heal every turn, if they so choose, and if you don't destroy them in a specific order, they'll tear you apart.
It might need a little balancing in the late game, but overall, if you have the first one, you can expect more of the same fun that was in the first one- or you could just outright buy the first one as well and play through that if you want to! If you didn't play the first one, that's still fine- you might not understand some of the story elements, but you'll like the great gameplay and all the fun!