Well, very little gets me as excited as Estee Lauder, and Knowing is my favorite of the house!!
I find it to be dark, sexy and brooding. It's very woody and leathery, floral, but not too sweet. And I think it tops the genre of dark, rosy chypres, which happens to be my favorite genre.
Not to mention, it's a Bernard Chant creation, and I love all of his fragrances!
Other notable dark rose you might know, for reference are: Gucci L'Arte, Sisley Soir de Lune, Ungaro Diva, PG Corps et Ames, Jil Sander No. 4....
I'd agree that Montana's Parfum de Peau was on par once (It was DIVINE.), but it's been horribly reformulated, and the old stuff is hard to find AND hard to identify. Estee Lauder, the other hand, has not reformulated anything, and it's a delight.
And as Suga points out, it's not too expensive, so it's a safe investment.