Hmmmm, I have to say that I'm sort of shocked by people claiming that Nars is unblendable, especially over MAC. About a year ago I completely switched over to Nars eyeshadows, my MAC generally is left to the sidelines.
And I have a ton of Nar, lol! Certainly, I agree that there are a several of Nars shadows/duos that are less pigmented and harder to blend, but generally I find that their shadows are nicely pigmented, more natural looking (I find that they "melt" onto the eyelid), and easier to use.
I agree with Elecktra, Nars is for the grown up woman. I say this because instead of doing intense "looks" as I did when I was younger (spending much more time on my makeup), Nars is perfect for a woman on the go. I generally use a single shade or two, a little highlighter, and I'm ready to go eye wise. Because they are so pigmented and easier to blend, you can achieve the look your going for much quicker.
I admit that I do use the more metallic shades the most (ie. the green side of Habanara is the bomb, the blonde side of Indian Summer is my HG at the moment, and I was a huge fan of Night Life last winter as a single shade on the lids, paired with a little red lipstick.). I especially like to use their cream eyeshadows as a base for a evening look, intensifying the above looks.
The Nars products that I'm not such a fan of are their lipglosses, the lip tints, and their eye liners (if anyone has a idea to make them not smudge as much, please let me know).
But their blushes, loose powders, and eyeshadows are definitely my favorite over any brand.