Anyone who has been painting with oils for any length of time (or passion) is most likely familiar with the Williamsburg paint line.  This isn't the Grumbachers, Reeves, or even Winsor & Newton oils from your craft stores.  Even many small art supply stores don't carry it because of the higher prices for some of the pigments.  It is considered up there with the other top paints such as Old Holland, Harding, Blockx, etc...much higher quality of product and a much higher amount of top-notch pigment loaded with minimal oil/fillers/binders.  This doesn't mean that it's not wonderfully creamy to use, though.  It just means that when you squeeze out a small nut of paint on your palette, that an equal amount of separated oil doesn't ooze out first and puddle around the color.  While some people might be only familiar with using oil color straight from the tube and actually may prefer the thinner consistency of those oil paints, I much prefer a thicker, higher pigment-load product.  I always figure that I can quickly and easily thin it to the consistency (and flat, smooth-brushing capability) of thinner oil colors by using various mediums or turps.  But when you want to be able to see expressive brush strokes, it really helps to use one of the best.