In terms of expectations, Iron Man 2 started as a quite different beast compared to its predecessor. After all, the first film was "burdened" by a protagonist without the mainstream appeal of, say, Spider-Man, a director better known as a character actor (Jon Favreau) and a leading man whose career has been shaky to say the least (Robert Downey Jr.). As it turned out, Iron Man was just what movie audiences needed, becoming a surprise hit, cementing Downey Jr. and Favreau's reputations as go-to guys in the industry (with the former winning a Golden Globe for Sherlock Holmes and the latter hired to direct another comic-book picture, Cowboys and Aliens) and kick-starting a new on-screen Marvel Universe, no longer limited by the issue of rights belonging to different studios (with the exception of pre-established franchises like X-Men and Spider-Man, characters are now freely allowed to cross over, just like in the comics). How do you follow that? With a sequel that retains the same spirit, but goes further in terms of scope and ambition.

Set six months after the conclusion of the first film, Iron Man 2 shows Tony Stark (Downey Jr.) in a tight spot: since he came clean about his double identity, his fame has reached sky-high proportions, but with the consequence that the US government (here embodied by Garry Shandling's annoying Congressman) wants the Iron Man suit for themselves. Additionally, the very thing keeping him alive - the arc reactor that has effectively replaced his biological heart - is slowly killing him (radiation poisoning), and two very different bad guys - business rival Justin Hammer (Sam Rockwell) and former engineer-turned-supervillain Ivan Vanko (Mickey Rourke) - are planning ways to get rid of him permanently. Lucky for him, Pepper (Gwyneth Paltrow), Rhodey (Don Cheadle, replacing Terrence Howard) and new secretary "Natalie" (Scarlett Johansson) are willing to help, assuming Tony doesn't destroy himself in the process...

Sequels are tricky by definition, and Iron Man 2 is a particularly tough one to pull off since it not only has to satisfy as a standalone follow-up (however paradoxical that may sound), but also set up events for the other movies that will make up the expanded Marvel movie universe. It all started with Samuel L. Jackson's cameo in the first movie's post-credits scene (followed by Downey Jr. making an appearance in The Incredible Hulk a month later), and this time the actor is allowed more screen-time - heck, he even gets his name in the opening credits - to do his usual stuff and set up The Avengers (plus minor hints at Thor and Captain America) in an intriguing way, without ever giving the impression that he's stealing someone else's movie.

And that's the real key behind Iron Man 2's success: it is an Iron Man flick, retaining the original's winning combination of action and humor, thanks to Justin Theroux's witty script and Favreau's effortless direction. Like most sequels, it goes dark in places, but this isn't Nolan's Batman, meaning that a lighter mood generally prevails (see the alcoholism subplot). Like the first film, the follow-up is a bit of a let-down when it comes to the climactic showdown (again, way too long), but otherwise it delivers everything it promised: the special effects are flawless (Exhibit A: the Monte Carlo race track sequence), the laughs and thrills are evenly balanced and everyone in the cast is fully game, from Rockwell and Rourke's riotous double act to Cheadle easily filling Howard's shoes, not to mention some welcome extra material for the director himself, who gets to be as funny as ever in the always entertaining company of Johansson. As usual, though, this is Downey's show from start to finish, and he slips into Stark's skin so perfectly it's damn near impossible not to raise expectations for the next installment.

Bottom line: as a piece in Marvel's expanding cinematic world, Iron Man 2 is as satisfying as one could anticipate. As its own thing, it's a fun, energetic follow-up that confirms the charm of comic-book movies and, much like its printed counterpart, leaves the door open for endless new possibilities. In other words: bring on number three...