It's a rare Lutens, perhaps because of all the expensive ingredients. I had to stalk the website off and on before I could get my hands on it! I love it, it's truly a fragrant, silvery, crystalline iris fragrance. I haven't used it enough (blaming that on a large collection with too many choices) to discover all the facets of the fragrance, and interestingly enough, I've had slightly different experiences both times I've worn it.
In more wintry weather a few months ago, the cool quality of ISM was more prominent to me, not too floral, and imparting a cool, aware, pleasant state of tranquility. Today, I tried it on and in this hot weather, I could distinctly smell other notes as it developed: slightly aromatic (clove?) more floral, a hint of incense, maybe some resins and a trace of silky woodiness in the base, all coming together with the star - the iris - to form a lovely, fragrant composition. No doubt the next time I use it, I will discover other nuances I had not noticed before. Perhaps that is the quality of a great, iconic fragrance like this.
I should also mention that the amount I used may have played a part in my scent experience. Thanks to the bell jar, the quantity of perfume dispensed varies! The first time, I just got a light dab. Today, I tipped out more and got a larger amount. Yes, I know I need to order some travel sprays and stop trying to tip a small quantity out on my wrist. I probably applied too much today! So there are my thoughts on ISM.
Sounds like you've sampled a fair number of Serge Lutens perfumes. Which ones stood out to you?
Oh, and I moved this response to the Perfume Chat thread.