The presumably final installment in the "Iron Man" series (we'll see about that) and the first of Marvel's "Phase 2" precursors leading into 2015's sequel to "The Avengers," "Iron Man 3" is a disappointingly middling start to this year's summer movie season that, nevertheless, also serves as a fitting personal conclusion to self-deprecating scientist/entrepreneur/makeshift superhero Tony Stark (Robert Downey Jr.). Bookended with promise and vitality, the film is cursed by a full middle hour that all but completely perishes from its own meandering dormancy. When audiences come to see a motion picture of this ilk, they naturally expect to be thrilled and treated to spectacle; what they don't want is a long, meandering slog interspersed with only a couple action set-pieces that live up to expectations. What's the point of spending hundreds of millions of dollars on that when other films at a fraction of the price tag far, far surpass this one in excitement, momentum and grandeur? On the positive, at least it's a baby step up from 2010's messier, more ramshackle misfire "Iron Man 2."

Struggling to process all that he saw and went through during "The Avengers" (Aliens! Wormholes! Different universes!), Tony Stark has become an insomniac, tirelessly creating replicas of his Iron Man suit that he can now control while being physically removed from within the metal. Because of his inability to move on, a strain has been put on his relationship with Stark Industries CEO and live-in girlfriend Pepper Potts (Gwyneth Paltrow). Their discord, however, must be put on the backburner with the appearance of a terrorist known as the Mandarin (Ben Kingsley). When friend and former security guard Happy (Jon Favreau) is injured in one such attack in front of the Grauman's Chinese Theatre, Tony invites him for a one-on-one fight at his Malibu mansion, instantaneous putting himself and Pepper in immediate danger. Thought dead, his seaside home now destroyed, Tony hides away in Tennessee as he plans his next step. What he doesn't expect is that the Mandarin is not who he seems to be, the devious megalomaniacal strings being pulled by a jilted scientist named Aldrich Killian (Guy Pearce), who is now holding Pepper captive.

"Iron Man 3" opens vibrantly with a trip back to New Year's Eve, 1999, in Switzerland (scored appropriately to "Blue (Da Ba Dee)" by Eiffel 65), Tony's amorous escapades with botanist Maya Hansen (Rebecca Hall) interrupted by the advances of nerdy, awkward Aldrich Killian—a guy who holds a long-standing grudge when Tony stands him up. Taking over for previous helmer Jon Favreau, writer-director Shane Black (2005's "Kiss Kiss Bang Bang") and co-writer Drew Pearce continue to right some of the overblown, overstuffed wrongs of "Iron Man 2," at least for a few more minutes. The romance between Tony and Pepper once more has the easy chemistry they had in the 2008 original, while Tony's inner turmoil is understandable and well-played. Once danger hits close to home and Tony reacts by foolishly challenging the terrorist and announcing his address on public television, it's enough to make a person want to slap their forehead.

What follows once mass destruction inevitably strikes his abode is where "Iron Man 3" really loses its way, relocating Tony to a snowy nowhere-town in Tennessee and temporarily giving him a needless kid sidekick, the plucky, blue-collar Harley (Ty Simpkins). As our hero bides his time preparing his next move, the film starts to tread water. So long do the proceedings go without offering up any sort of notable intrigue or action that one begins to wonder if he or she is watching a superhero-laden popcorn movie or a talky chamber piece. And then, at long last, just as hope is seemingly lost, the picture instantaneously jumpstarts to life with a dizzyingly bravura sequence in which an Air Force One flight disaster leads to Iron Man having to think fast and find a way to save eleven passengers free-falling to their deaths. Decked out with flawless effects and stunt work and a palpable edge-of-your-seat threat, it's enough to leave a person wondering why the previous sixty minutes (at least) have been so dreary and uninspired. Continuing from there, the non-stop climax is suitably satisfying, even if it does fall back on the tedious cliché of being set amidst a ship barge full of giant crates. Is that really the best director Shane Black could come up with?

By now, Robert Downey Jr. and Tony Stark are as synonymous as a hand inside a well-fitted glove. No longer having to worry about his previously deteriorating health, his concerns have now been replaced with a sort of post-traumatic stress stemming from his discovery that there is more—much more—out in the universe than just little, ol' Earth. It's not all moping around, though; Downey Jr. is at his best when he's delivering a barb and generally acting cool under pressure. There is good and bad news when it comes to Gwyneth Paltrow's (2010's "Country Strong") role reprisal of Pepper Potts; she is treated no longer as the uptight nag she was in "Iron Man 2," but is marginalized for too long in the second act, virtually disappearing completely until the finale. Her absence is certainly felt. As Tony's buddy Col. James "Rhodey" Rhodes, a miscast Don Cheadle (2012's "Flight") still cannot come close to making the impression that Terrence Howard did when he originated the part; Cheadle uneasily fits into the story and, aside from the U.S. Air Force repurposing his War Machine Armor as the red, white and blue Iron Patriot, has little to do. New cast members are functional, but humdrum. Guy Pearce's bad guy is wholly forgettable in comparison to his vital, spiteful, Oscar-robbed performance in 2012's "Lawless," where the very parting in his slick hair was more of a standout than anything seen here. As Maya Hansen, who holds ties with Pearce's Aldrich Killian, Rebecca Hall (2012's "The Awakening") is put to no special use at all. And, as the Mandarin, Ben Kingsley (2012's "The Dictator") is a sobering vision of sociopathic radicalism until his character takes a sharp turn toward over-the-top, reminding in a bad way of his villain in 2004's embarrassing "Thunderbirds."

"Iron Man 3" completes Tony Stark's journey in finding himself—as a person, as a philanthropist, as a protector of the people—and in this regard, the film fulfills its duties and ends on a graceful note that should serve as a franchise capper if Downey Jr. decides not to come back for a third sequel. Judged as its own individual entity, sadly, reveals a film that doesn't live up to Marvel's best features, feeling scattershot and stretched-thin and distinctly unoriginal. Slow to get going and then too late to recoup, director Shane Black has made a polished film, but one that is alternately too jokey, too ruminative, and too separated from even the reality set up in these movies (a fire-breathing human? Really?) to find a comfortable tone. "Iron Man 3" might not be a total bust, but it does result in one big "meh."