Since I'm only 5" the costume was really slouchy in the leg area, but it didn't ruin the look. The fabric soft and warm (definitely wear in a place with AC or during cooler months). I think the "regular" size would fit adults S-XL. My otter rock stayed perfectly buttoned in place the whole time.
at first i was annoyed that this was a little more expensive than other onesies, however the quality is FAR ABOVE that of cheaper onesies. the fleece is thick and warm, the wings are double sided, and the features on the face/head are well done, not flat. no corners were cut in the design and construction and i really value that. very warm and fun to wear :)