The poem starts with a familiar saying, "Never judge a book by its cover," and then turns it around. The speaker agrees with it, but not in the usual way. Instead of a plain cover hiding a wonderful story, here the cover is gorgeous and the story inside can't match it. The plot, setting and characters all fall short.
The "books" start to feel like a stand-in for something else. Judging by the way the poem talks about climaxes that turn out to be "downfalls" and stories that never reach an ending, the speaker could be thinking about people or lives that look impressive on the outside but disappoint or break down underneath. That reading is an inference, since the poem never says it outright.
The mood is quiet, disappointed and a little bleak. The speaker sounds weary rather than angry, and the last lines, about stories that "don't even make it that far," leave the poem hanging, almost like an unfinished book itself.