The mistake I made here is reading all the reviews where everyone said to go up a size.  I am a straight size medium but based on reviews I ordered a large.  Mistake.  I can wear it...it's a great shirt.  Large is too big though.  So I ordered a second one in medium and it fits like a charm.

I personally recommend you stay with your regular size.  If you are a medium...order a medium.

I love the shirt.  It will be great for layering under flannel shirts..etc.