This is a Henley:
I have always thought they looked horrible, and unfortunately during the grunge era they became more than underwear when such style icons as Eddie Vedder wore them under their flannel logger shirts. Anyway, I really like the 1/4 zip and full zip sweaters that are popular now. I have been looking for them for a long time and unfortunately it's only when they trickle down to the masses that I can consider buying one in merino or cashmere, so I will probably snap up a couple this season. Unfortunately the ones I have found in "medium", as I was ranting about earlier, have all been 48-50" in the chest, about 6-8" too big for my taste. I wish "mainstream" designers would get it through their head that sizes are supposed to mean something.
I generally agree Henley shirts don't look good, but as is true for every garment, it depends on the fit and details. I think one such as done by Christopher Bailey for Burberry looks relaxed yet stylish.