I think Jeff has got it right. Not essential, but the better patterns do break up your outline.
Most importmant to me is the clothing itself. If it is quiet, warm or cool, depending on the season, comfortable, sheds burrs, fits well to allow layering underneath, and has pockets of the right size in the right places it works for me. Hunting clothes are designed for what we do, and the good stuff does it very well. It generally does come in camo, and that is good too, but the other things come first on my list when selecting clothing.