As a study of rhetoric, Eunoia falls much more into the craft category than most of its contemporary brethren. It challenges not what rules we have (the standard provocative method) but what rules we can have. I find this a far more interesting pursuit in a world that has been trying so hard to break boundaries for longer than anyone alive can remember now.
Christian Bok runs in the exact opposite direction, forcing not only the obvious constraints on vowel usage into his poems but thematic and mechanical ones as well. Each chapter has a section devoted to the sea, to debauchery, to writing, and to a feast among other things; according to his addendum, each chapter contains at least 98% of the possible words for its vowel (the exception being "E", where he excuses the other words as "vocabulary unsuitable for the retelling of the Iliad" which he pulls off in that chapter. His apology? Another poem at the end of the book containing those remaining words).
These restrictions certainly make a mess of things sometimes and the subtext of any particular passage can only go so far with such a bound vocabulary, but seeing what can be accomplished under this scheme is beautiful in itself. It's what lyrics seem like they should be striving for: a perfect correspondence to the form of the music they flow through.