Curator, Ann Temkin: What matters to Matisse isn't some realistic description of what a ring of dancers would look like, but the way that this ring of dancers would fill the dimensions of this rectangular canvas, and thus you have things happening like the very long reach between the two dancers in the foreground at the far left and then at the bottom right, where you see their arms reaching and barely touching each other's and, in fact, the way in which the woman on the far left's right hand is painted, it almost looks like it's unfinished, but for Matisse, that was enough.
Matisse painted it in a very quick amount of time, less than a week, and he did something that was so shocking, in a sense, in making a painting that's essentially a few colors.
Another radical thing is that the sky and the earth are not given any detail whatsoever. It's just a purely flat expanse of this one blue color and this one green color, painted in such a way that you realize that you're not in some kind of specific place that can be identified, but rather some kind of ideal place in the mind's eye.