The beauty of "Iron Man 2" is how it carefully sustains the joyful superhero elements established in the first film, released a mere two years ago. The problem with "Iron Man 2" is that is also inherits the original picture's absence of hard-charging exhilaration, with the sequel as moderately uneven as its blockbuster predecessor. It's a small quibble, but one that tethers an otherwise wildly entertaining and intermittently thrilling action-adventure to the ground.

Tony Stark (Robert Downey Jr.) has become Iron Man, but Iron Man is slowly killing Tony Stark. Learning the palladium in his Arc Reactor power source is poisoning him, Tony is panicked to find a cure, signing over Stark Industries to his partner and romantic fixation, Pepper Potts (Gwyneth Paltrow), to buy him time. The government wants Tony's Iron Man secrets to build a new line of defense, while Russian physicist Ivan Vanko (a scene-stealing Mickey Rourke) has already established a threat, out to kill Tony for the rough treatment his father received at the hands of Stark Industries. Also in the mix is Tony's corporate rival, Justin Hammer (Sam Rockwell), who wants to squash Iron Man and build his own army of battle suits with the help of Ivan, who doesn't share his boss's quest for profit, hungry only for revenge. Complicating matters further is Tony's pal Rhodes (Don Cheadle), who's been ordered to bring the Iron Man technology back to his military superiors, and Natalie (Scarlett Johansson), an enigmatic employee of Stark Industries with a startling set of martial art skills.

To give the sequel a refreshed sense of purpose, screenwriter Justin Theroux has whipped up a buffet of characters and motivations to present the loyal with much to munch while feasting on this highly anticipated follow-up. The full-court-press of fresh dramatic developments would cripple most filmmakers, but director Jon Favreau keeps it all comfortably contained, working around some extensive narrative loops, yet keeping his eye on the prize: red-hot Tony Stark action. The blowhard, smart-ass industrialist isn't handed a back seat to his own vehicle, which is one of many things I enjoyed about "Iron Man 2." Even in the face of this dazzling ensemble and deeper budgetary pockets, Favreau keeps his wits about him, embarking on a snappy second round agreeably mindful of what clicked before.

To shoo away the rehash blues, "Iron Man 2" turns to domestic matters, giving us a Tony Stark facing his mortality, confronted with family business he's never thoroughly investigated, only dutifully organized out of obligation. The centerpiece of the sequel is the Stark Expo, a dream construction project of his Disneyesque father (played by John Slattery), which leads to unanticipated connections to a past Tony has always disregarded. It's a satisfying psychological element layered into the script that allows the character a chance to relocate his purpose, while also playing into his growing ills, including a newfound dalliance with alcoholism. At the very least, "Iron Man 2" is game to try on a few new shades of torment for Tony, giving the film something to do now that the element of superhero surprise has been eliminated.

While the tangled emotional web for Tony is necessary, sorting out the whole subplot weighs down "Iron Man 2" during its second act -- curiously, the same swollen atmosphere blunted the sugar rush of the original picture as well. The mid-movie brakes are especially evident due to the film's explosive opening, establishing Ivan as an electric-whip-cracking nemesis who greets Tony in the midst of the Grand Prix racing event in Monaco, disrupting the festivities with a calculated plan of humiliation and murder, brought to life by Tony's own technology. There's a stupendous closer as well, which combines all the elements of Theroux's writing into a final swell of sonic-boom heroism and repulsor-ray chaos, returning to the basic appeal of Iron Man, while playing around with a new creation in Rhodes's battle suit, nicknamed War Machine. The picture opens and closes with breathless feats of widescreen ferocity and economical characterization, making the fatty tissue in the middle too chewy, or just downright unappealing, as viewed in a gratuitous showdown where an intoxicated Tony and a dutiful Rhodes square off for what feels like a full year in their respective super-suits.

When "Iron Man 2" stands up straight, it's all sorts of fun, scored to a nice range of classic rock hits, and bats about 60% in the improvisation department, with Cheadle clearly out of his league. It's still the Downey Jr. Show, and the manic actor steers the ship with expert smarm, playing superbly off Paltrow, who shines once again as Tony's confidant and panicky critic. Samuel L. Jackson enjoys some fizz as S.H.I.E.L.D. director Nick Fury (the film takes a few moments to pour in plenty of Marvel foreshadowing), Rockwell beats the creep drum with ease as Hammer, and while lacking a significant role, Johansson gets in some compelling kicks as Tony's gymnastic assistant; it's a character seemingly created to payoff in a future sequel, which appears to be the case with much of "Iron Man 2."

Much like the original picture, "Iron Man 2" doesn't ultimately fatigue, it just lacks a singular detonation to make it soar like the best superhero movies are capable of. It's rock-solid summer entertainment and is gifted an excellent cast to bring it color and verbal lashes, but once again Tony Stark comes to the big screen absent a few significant beats of awe.