Although certain Oxford Companions have been flawed -- that to "Film" had a lot of errors; and in my minority opinion that to "English Literature" wastes far too much space on tangential matters -- most are informative, authoritative, and endlessly browsable. This new Companion to Turner belongs among them. With all the detail it offers about Turner, it's a substantial work and one that will only appeal to those who already have one or more collections of his works; it's understandable that this volume does not duplicate these; if it did, its weight and size (and unwieldiness) and price would rocket.
My only disappointment so far is admittedly peripheral: why does such a scholarly (and expensive) volume not come in the black (or immensely dark blue) cloth that OUP gives to most of its hardbacks?