Conjuring consistency is tough for those adapting Harry Potter novels to film. Four different directors — Chris Columbus, Alfonso Cuarón, Mike Newell and, now, David Yates — all have thrown different spins for author J.K. Rowling’s ever-expanding narratives.

One thing that’s held up, though, is that the odd-numbered ones all have been rough spells. Harry Potter and the Sorcerer’s Stone was a fittingly playful debut that slavishly adhered to its text, and Harry Potter and the Prisoner of Azkaban was a beautiful but boring third installment.

As the films go, Harry Potter and the Order of the Phoenix is a stiff series low. It’s severely streamlined, as the 896-page hardcover novel is packed into a 138-minute running time. The wizards, though, can’t wave off irony with their wands, as the shortest film so far feels the longest.

After a stout start, it’s a talky, dragging affair ballooned by exposition that criminally shortchanges many in its British cast of greats. (Really, the great Emma Thompson couldn’t have thought this was all there would be for googly-eyed divination Professor Sybill Trelawney.) This adaptation’s cruelest casualty, though, is the thrilling rush in its tale of young-student rebellion.

In the novel, that anti-authority streak drew snickers that ran concurrent to its mercilessly human descent into steely themes of death, sacrifice, disappointment and temptation. Aside from one so-so montage and a good table-turning line from Harry to the latest despotic teacher, there’s not much dark sarcasm in these Hogwarts School classrooms.

Drawing from sturdy source material, Yates and new screenwriter Michael Goldenberg still find some lively moments. In his best moments, Yates blends Barry Sonnenfeld’s visceral movement with Terry Gilliam’s absurd surrealism. And although he proves nowhere near as wise an adaptor as former scribe Steve Kloves, Goldenberg has fun adapting Dark Arts teacher Dolores Umbridge.

The Spanish Inquisition wore red and died off in the 19th century, but its spirit lives on, dressed in Umbridge’s pink and purple. Played by Imelda Staunton (Vera Drake), Umbridge announces herself with passive-aggressive giggles before climbing atop a bully pulpit for education reform. Even Severus Snape (Alan Rickman) wilts at her words, and Staunton cuts loose and has a blast.

She’s the central figure in a dictatorial coup at Hogwarts School of Witchcraft and Wizardry. Its governing body, the Ministry of Magic, dismisses as pish-posh Harry’s assertion that evil Lord Voldemort (Ralph Fiennes) has arisen again. As a baby, Harry (Daniel Radcliffe) survived a Voldemort attack that took his parents’ lives and forged a yin-yang bond with the noseless baddie.

An emissary of the Ministry, Umbridge takes over Hogwarts’ perpetually vacant Dark Arts position and immediately abolishes all application of magic. Consigned to textbook study, Harry and pals Hermione (Emma Watson) and Ron (Rupert Grint), channel the spirit of a long-lost legion known as the Order of the Phoenix. Designated to battle Voldemort’s army all those years ago, it has re-formed in secret meetings led by Harry’s fugitive uncle Sirius (Gary Oldman).

Harry reluctantly takes the lead of the Order’s young-army offshoot, and discovering his potential in leadership provides the best moments in an otherwise inert story for its title character.

Personal legends aren’t great when suffused with so much death, luck and uncertainty as Harry’s, and Radcliffe knows how to measure out reconciliation with destiny. Radcliffe — now with short hair and some gun-show muscles — continues his realistic, invisible inhabitance of this icon.

The film is best when it sticks to him and his camaraderie with Ron and Hermione. Although Harry’s much-ballyhooed smooch with Cho Chang (Katie Leung) is an overblown moment, it provides a brief spark of connection among this fast-friend trio crucial to Harry in the fiery climax.

That clash-of-the-titans showdown between Voldemort and wily wizard mentor Dumbledore (Michael Gambon) is a rare moment when the effects feel special. Like Azkaban, there’s too much dimly lit dark-forest action, and most creatures are shown either in shadow or in the style of Shrek. (After this and Van Helsing, it must be a rule that CGI giants all must look like the green guy.)

Phoenix is even more of a crushing disappointment coming on the heels of the best movie yet, 2005’s Harry Potter and the Goblet of Fire. Newell’s film took inspiration from Rowling’s zesty literacy. In the wrong hands — and it can’t be a good sign that Yates is returning for 2008’s Harry Potter and the Half-Blood Prince film — her saga can be as lumpy and bland as gray porridge.