I think this powder is best as a setting powder, not as a foundation/base. Now used over the top of your foundation, this powder gives the most airbrushed effect I've ever seen. I even prefer it to my Laura Mercier setting powder and MAC studio fix powder (which are my other favourite products I use to set or touch up with. The only time I get asked what I have on my face, is when I am wearing this and it photographs like you've used a filter.
Now the things I don't like are 1) the price. 2) The colour selection. I am golden under toned, and am very limited to the shades I can get. I mostly use 117 which is Golden Ivory (I'm NC30) and slightly light, but the next shade up is 123, golden sand and this is WAY too dark. 3) It definitely oxidises a bit, which is why 117 works better on me, and finally 4) It breaks real easily. As in the powder - especially once you've hit pan with a good sized well. Annoying.
However, all things aside, I will ALWAYS have one of these, especially for nights out etc, just because it makes my skin look so flawless and prefect.
Just for reference, I have combination skin.