I own one, and it's a "grail" lens for me.
I don't consider the 180mm as a good portrait lens. For one thing, it's a roughly 4x lens (43mm diagonal), and compresses the subject a bit too much. For portraits, the 135mm is the maximum (head, and head and shoulders), and a 105mm for waist length (Some folks like the 85mm class, since it's 2x).
The 180mm makes a fine lens for journalists, along with the 105mm f/2.5, and a 50mm f/1.4. I use mine a lot for landscape when I can't get really close. It's most often paired with my F3 and FM2n.
It's value is that it's a prime lens. I do have an 80-200 f/4, but I'm still of the opinion that the best lenses, especially from the AI and AI-s era, are the primes.