You play as either of the twins Reynold or Wren, and the game kicks off with the other sibling being kidnapped by mysterious monsters that just can't get enough of candy. Of course your sibling decided to dress up as a giant candy during halloween, and it's up to you, and two friendly kids from the block, to find and rescue your lost twin before it's too late. The nasty monsters are invading your local neighbourhood, mall and countryside to satisfy their sweet tooth, but luckily you have powerful costumes to switch into when it's time for battle.
The costumes, which serves as your "equipment" (for lack of a better RPG reference), come in different flavors, and range from knight to vampire (and ninja!). It's wacky and delightful to watch your characters switch into their respective role in battle. One minute you're out walking about, wearing nothing but a cardboard box claiming to be a knight in shiny armor, and the next moment when you encounter a monster you swing that sword and shield like you've done it all your life! You really have no idea if all of this is in the child's mind or not, but frankly you really don't care. It's all very clever made, and you quickly make it your personal goal to find and use every costume there is.
The gameplay is very simplistic, and while the game is obviously aimed at a very young audience, it sometimes drags on a bit. There really isn't much more to it than running around, picking up very simplified quests, encounter a battle, and then enter a traditional "attack > block > use superpower > win"-fight. However the artstyle, storytelling, and pretty much everything surrounding all of this is so well made you quickly forget you're playing something juvenile. Hell, I'm 28 years old when I'm writing this, and I simply couldn't put the game away until I finished all of it.
The length and replay value might be a wee bit disappointing, looking at the (currently) $15 pricetag. Finishing the story and all of the achievements took me around five hours of nonstop playing, but as I said those five hours were filled with smiles and feelings of a childhood almost forgotten by now. If you have younger children in your household I definatly recommend picking up Costume Quest, if not for the excellent story and artstyle, at least as a first attempt of introducing RPGs to the little ones.
(Apologies for bad spelling, as my native language isn't English)