What makes a good constitution? Standoffs and horsetrades, frozen in time. (James Burnham said, in his wisest book, The Machiavellians, that freedom falls to all of us as a by-product of the contentions of elites).
King John v. the barons gaves us Magna Carta. William of Orange v. his new parliament gave us the settlement after the Glorious Revolution. Large states v. small states, and federalists v. anti-federalists gave us the Constitution and the Bill of Rights.
Nothing is perfect and most of it will have to be worked out in practice, but the draft looks as good as anyone could reasonably have hoped. Congratulations to the Iraqi pols–for behaving like pols, not messiahs or mobsters.