The New York Times notes dog cognition expert Alexandra Horowitz's piece in The New Yorker questioning whether pets enjoy dressing for Halloween.  An excerpt from The New Yorker:

"The philosopher Thomas Nagel famously asked, in his titular essay, “What is it like to be a bat?”: what, in essence, is the subjective experience of a non-human animal?
 
Around this time of year, one might revise Nagel’s query to 'What is it like to be a bat—dressed in a Superman costume?' Or, more accurately for of many contemporary American pets, 'What might a dog (or cat or hamster or parrot) think of being costumed and festooned, or forced to don a hat and fake mustache in our celebration of Halloween?'
 
Inasmuch as I can speak to the experience of any animal (including members of my own species), my answer is 'The dog, he does not like it'."