The Parfum version of Terre d'Hermès is an interesting one. Mainly because I can't think of other male-marketed perfumes being sold in "Pure Perfume", "Parfum" or "Extrait" concentration...
That being said, this version does have it's own merits. It wears closer to the skin, it's richer, it doesn't have the sillage of the other one (it won't fill a room with smell), but you will notice it for a long time. Two or three sprays of this will last for over six hours, and it holds itself very well.
You get a much smoother, denser and richer smell with this one, and a lot woodier. The woods here are quite prominent. Whereas the original was orange and grapefruit, this is orange and cedarwood, along with patchouli and vetiver. There may also be geranium here which adds to the "flinty" impression. Basically the Iso-E-Super (which Jean-Claude Ellena seems to love using) is more prominent in that it gives the Parfum a much deeper base to the whole composition. Another thing is that (as expected with a Parfum) this is linear. So you don't get the transitions experienced by the Eau de Toilette. This could either be a good or bad thing for you, but it is what to be expected from a higher concentration.
Overall, I think there is a place for the Parfum. If you are someone who likes spending more to feel more "smooth" or "polished", or want it to last longer, or like "heavier" scents, this could be an option. Of course having a Parfum is also a luxury, so you have to expect to pay more. I would describe this as mainly smooth and linear, and could be worn by a woman, if the same woman could also wear something like Encre Noir by Lalique. I could safely say that Terre d'Hermès Parfum is (very) similar to Encre Noir, just with a composition focused around citrus. The strong vetiver, cedar and Iso-E-Super are all there, and it has a "serious" tone... at least to me anyway. Again, a little different than the Eau de Toilette in tone (not in character), but it depends if you prefer to spend more money for that difference.