I studied with him in the early 90s when I was an undergraduate at Yale and even before that his book RHYME'S REASON was one of my early primers on poetic forms.
Here is a clerihew about him by another of my Yale professors and his colleague Marie Borroff, which I think embodies both his love of wordplay and of form:
WrOte a pOem shaped like a cOllander,
With hOles cOmpOsed Of rOws
and rOws Of capital O's.