Critical looks at 'Oz'; The Wizard of Oz, by L. Frank Baum, with pictures by W. W. Denslow. The Critical Heritage Series. Edited by Michael Patrick Hearn. New York: Schocken Books. 306 pp. $19.95.

''The Wizard of Oz,'' introduced and very ably edited by Michael Patrick Hearn, launches Schocken Books' Critical Heritage Series. This edition includes not only the complete text of L. Frank Baum's first Oz book and 24 of the original drawings by W.W. Denslow, but some 18 critiques of Baum's writing. The cumulative effect is almost an overdose of Oz, even for a lifelong devotee of the books. One wonders just what good old super-imaginative Frank Baum might have thought about the literary and psychological dissection of stories he wrote simply to give children pleasure.