The Anxiety of Influence, Harold Bloom
Axel's Castle: A Study of the Imaginative Literature of 1870-1930, Edmund Wilson
The Wound and the Bow: Seven Studies in Literature, Edmund Wilson
I've been taking a break from primary sources to enjoy three excellent books on books.
The first is Harold Bloom's seminal Anxiety of Influence, by the blustery, brilliant, highly opinionated professor and professional Shakespeare worshipper.
The second is by the notable critic Edmund Wilson and features critical essays on W.B. Yeats, Paul Valery, T.S. Eliot, Marcel Proust, James Joyce, and Gertrude Stein.
Also by Wilson is The Wound and the Bow, with essays on Dickens, Kipling, Wharton, Hemingway, Joyce, Sophocles, and Casanova.
All three are marked by excellent writing and rare insight, hallmarks of criticism as a literary endeavor in its own right.