Just got this costume.  It's okay - pretty cheaply made, as I expected.  I ordered a size 10-12 for my (large) 7 year old and it fit him perfectly.  He usually wears a medium in shirts and a 7 in bottoms so I was surprised.  The mask is pretty flimsy - it's secured by a thin piece of elastic with a small piece of velcro.

My son likes it.... let's just hope the costume lasts until Halloween!