Their site is pretty good.
Pretty descriptive and at least usually has a decent photo or two to ensure parts at least look right.
Usually a lot of choices too.
From the cheap chinese that most others offer, mid-range, then better quality.
Even list by costs mostly.
Can usually find chinese stuff a pinch cheaper elsewhere by the time shipping adds in, but I have had pretty good luck with them the little I have gotten from them.
A couple other sources get stuff to my place quicker, so if all is the same I use them.
But nothing bad to say about Rock Auto.