Dan Meyer complains eloquently that paper can't do what screens can to help students enter into a problem-solving process. It's not about the books getting worse, but about other options getting better.
Folks who want us to teach in a conventional way decry the 'reform' math texts that have been coming out for the past few decades. I generally disagree, but I've seen some folks I respect complaining, so I listen and try to learn.
I'm trying to escape from textbooks, but that takes years of experience, and lots more support than elementary teachers get these days.
Here's an entirely different take on the textbook question, from inside the publishing industry. It's a bit scary how badly schools are being used and abused in the quest for more profit. (Of course, there's also lots of money to be made by the publishers at the testing end of the schoolroom, too.)
[Edit on 2-27: Here's another post about publishers making money off education. More of a rant.]
There is so much that schools could be, but right now they are being shackled, and are not providing healthy environments for kids and their learning.