David Wiley had an interesting blog post last week that touched upon this idea of "judging textbooks from commercial publishers perspective". This is a lengthy quote from the article. It is a good read.
On Quality and OER
Beyond issues of accuracy, when publishers, their press releases, and the media who reprint them say “quality” with regard to textbooks and OER, they actually mean “presentation and graphic design” – is the layout beautiful, are the images high resolution, are the headings used and formatted consistently, is the book printed in full color?
But this is not what we should mean when we talk about quality. There can be one and only one measure of the quality of educational resources, no matter how they are licensed: How much do students learn when using the materials?