Keats's poetry is collected in a definitive edition printed by the Oxford University Press called The Poetry of John Keats. The first edition was published in 1939 and it was updated for the 1958 second edition (minor corrections are noted in the preface by H.W. Garrod).
Well-known British critic John D. Jump published a short volume in 1974 called The Ode, which traces the history of the poetic form from ancient Greece to the twentieth century, telling readers just about everything anyone would want to know about odes.
Another famous critic, this one American, is Cleanth Brooks, who published a book about poetic forms in 1947 called The Well-Wrought Urn. The title, of course, refers to this poem, although the author's study of Keats is only one out of eleven chapters. This book is invaluable to any student of formal poetry.
For readers who are interested in both Greek mythology and modern literature, Lilian Feder's 1971 Ancient Myth in Modern Poetry looks mostly at twentieth-century authors, starting with Freud and Jung, and at how ancient stories are probably more "alive" now than they were for Keats. Poets studied include Yeats, Pound, Eliot, and Auden.
The Use of Poetry and The Use of Criticism, a 1933 collection of essays by brilliant modern poet T.S. Eliot, has a chapter about Shelley and Keats that gives a smart contemporary perspective to the two Romantic writers.