In hindsight, the way WB handled the directorship of what became their most lucrative investment (and THE ongoing movie event of the previous decade) was a bit risky, especially after Columbus decided not to stay on for the whole enterprise. What followed was a series of the sort of interesting - even bold - choices that most studios don't go anywhere near when hundreds of millions of dollars are on the line. The studio displayed massive confidence in their brand, taking the chance on directors who'd never crafted a tentpole in the hopes of shading the HARRY POTTER films with something unique. The idea of several visions for a single series doesn't usually sound like the best approach, but in a franchise dealing with growing children and a new year of school every entry, it's actually a rather ingenious method.
What's more, each director took it upon themselves to act as an early guide for their successor, from Columbus to Cuaron to Newell - all would show rough cuts of their movies to the "next man" or help walk them through their own approach to the franchise. This close cooperation (along with consistent Art Direction courtesy of Stuart Craig and Stephanie McMillan) is undoubtedly one of the elements that keeps the franchise feeling like one continuous story in a single world, rather than several disconnected films.
We saw how this helped create a sense of cohesion between the first four films in Part 1 and Part 2 of the retrospective. But something was still missing, and with the fourth director the series finally found it.