Is there anywhere I can find reliable reviews of popular textbooks?
I am not aware of any specific aggregator of textbooks review. But... reading reviews on Amazon may help. (By reading I mean actually reading, not just comparing average scores;  especially reviews with non-extreme grades. Usually they also gives some context the reader's position and motivation.)

Also:


some journals have a section with book reviews,
some researchers and lectures write blog posts, reviews or suggested readings,


however, each single review is only a single data point.

But once you focused on a few books, there is no shortcut to actually looking at their content and deciding whether it fits your course, approach, taste, etc.