With so much variance in sizes, it was nice to get a medium on a first try.  Not a super large small, or a small large, but a medium medium.  Snug but not tight, not overly long.  CAUTION: don't judge size until you wash it.  It shortens up massively.  I love the fit of this shirt in medium (5-11, 165 athletic shoulders), the only drawback is that it is slightly thicker than the average shirt (and thus warmer).  A better shirt for fall/winter.  And yes, the neck plunges lower than the nauticas which make it look better if you open your collar.