They're exactly what I wanted, and arrived on time and in perfect condition.  I will say two things:
1.  Because they are painted with a flat paint, they are more "dark brown" than "espresso".  Generally speaking, an espresso finish suggest that there's a wood grain visible - that is not the case with these shelves.  I mention this for those looking to match finishes in their homes.
2.  One detail left out of the installation instructions is where to place the mounting brackets in relation to the front/back of the shelf.  For best stability, I'd recommend placing the brackets towards the front edge of where the shelf will sit, as opposed to further back towards the corner.  This means that the brackets will be more visible once the shelf is installed, but sturdier and able to safely support more weight.

Thanks, Wayfair - this is the first time I've shopped on your site, and I'll probably be back!