I am 5'6" and I am a size 8 to 10 (depends on the brand). I purchased a small and the fit is great in terms of size, the pants are comfy without being baggy and the shirt is fitted, but not tight.

The shirt is a double layer knit - I find this to be the perfect weight for a winter PJ (I live in New England and it gets cold).  If I wear something heavier I'll be too hot under my blankets, but too light and anything that ends up exposed is cold.  I was very happy with the weight.  The pants are a lightweight fleece, again, not too thick - in my opinion the perfect level.

The pattern on the front is super cute for both sets I ordered.  It has an applique sewn on, the quality seems to be high. My only negative (and the reason it got a 1 star review) is that the pants are just a bit too short.  When sitting around on the couch with my feet up, they expose quite a bit of my lower leg. Everyone is different of course, but at 5' 6" I'm pretty average and generally I do not have a problem with the length of pants, so if you are taller, these pants are definitely going to be too short for you.  They are OK for me, but they lose a star for it, they should as long as regular pants.  If you are a bit shorter though and often find things to be too long for you, this may be a plus.

Overall, they are a good buy, I'm looking for another sale so I can get more. :)