I've been very frustrated with the coverage of this story, because very rarely do the news stories actually say just what the textbooks teach. The "Moses was a founding father" comment came from a critical history professor characterizing the books, not from the books.
That's not to say the books are good. I'm sure they're pretty bad. But I have no way of judging how bad, because we are only told the summaries of their harshest critics.
(Some of whom are fairly ignorant themselves. For example, one of the professors who has been most critical of mentioning Moses also lambasted them for saying William Blackstone was a big influence on the Constitution, because "Blackstone believed all societies should require some form of absolute, unchallengeable sovereign power." That may be true, but it's patently obvious that Blackstone was a major influence on the Constitution and the whole legal climate in which it was written (not for saying that, but for delineating the legal rights of Englishmen, the law of property, etc.)
So actually I really appreciate 2WL's post, which is the lone one I've seen that does provide some detail.
Having skimmed it, I'd say I agree with many of its critiques (though it's false that the books say or imply that Moses was a founding father). The document is wrong to contest the textbooks in pointing out that "separation of church and state" does not appear in the Constitution -- that's an important thing to understand even for those who support such a separation, since it has huge influence on how it is interpreted through the clauses that actually do appear; nor is its application to American law in the least uncontroversial, even on the Supreme Court. So it's a perfectly reasonable thing to say.
Among the rest, a lot of the criticisms are fair, several nitpicky, but generally they probably are errors. Unfortunately, many or most American textbooks are rife with such errors. These ones did not stand out relative to other textbooks I've seen reviewed, though the errors probably had a tendency to be those a careless conservative would make, rather than those a careless liberal would make (as in some textbooks) or that somebody careless of indeterminate persuasion would make (as in still others).
So, too bad this is all so politicized. The left will rightly scream about the conservative errors and skew, while nobody much will care about the fact that the books are terrible to begin with, and still would be if there were no skew.