We've seen what the fanboys think, so now how about the actual critics?
While Downey consistently steals the show with his desert-dry delivery, each actor in the freshly re-energized cast gets the chance not only to crack wise, but to touchingly express the self-doubt that lies at the heart of every superhero.--Justin Chang, Variety
With only one feature directorial credit to his name, the middling 2005 sci-fier Serenity, Whedon of Buffy fame would not have been the first name on most people's lists to tame a potentially unwieldy project. But from a logistical point of view alone, Whedon imposes a grip on the material that feels like that of a benevolent general, marshaling myriad technical resources (including an excellent use of 3D) while, even more impressively, juggling eight major characters, giving them all cool and important things to do.--Todd McCarthy, The Hollywood Reporter
Crucially, the wise-cracking id of Robert Downey Jnr's Iron Man is balanced out by instilling a hearty dose of fear in one of the team's central figures, thanks to a beautifully honed performance by Mark Ruffalo. He plays Bruce Banner – the brilliant scientist who turns into the uncontrollable colossus Hulk when angered – as a man afraid of himself.--Henry Barnes, The Guardian
With Earth’s Mightiest Heroes™ gathered, they needed a good villain to fight, and Loki certainly fills that void. He’s even more devious and devilish than his introduction in Thor and Hiddleston thoroughly owns the role, imbuing it with pure, malicious delight.--James White, Empire
Joss Whedon’s lavishly enjoyable, chewily-titled film (the branding’s there to warn British cinema-goers that John Steed will not be making an appearance) is an assemblage of everything that’s good about contemporary popcorn cinema; just as importantly, it’s a rejection of everything that isn’t. Avengers might be short on bright ideas of its own, but co-writer and director Whedon has a magpie’s eye for stealing other people’s, and an enviable knack of improving them.--Robbie Collin, The Telegraph
Casting's been a strength of the Marvel movies, and everyone who's returning matches their earlier engagements -- any fear that Downey Jr. might be phoning it in is misplaced, as he's actually stronger here than he was in the last "Iron Man." For the first time, Samuel L. Jackson feels engaged, rather than cashing a paycheck, and Scarlett Johansson's gone from dead weight to one of the highlights of the film (honestly, she's almost revelatory here).--Oliver Lyttelton, The Playlist
Sources: 1, 2, 3, 4, 5, 6, 7
While Downey consistently steals the show with his desert-dry delivery, each actor in the freshly re-energized cast gets the chance not only to crack wise, but to touchingly express the self-doubt that lies at the heart of every superhero.--Justin Chang, Variety
With only one feature directorial credit to his name, the middling 2005 sci-fier Serenity, Whedon of Buffy fame would not have been the first name on most people's lists to tame a potentially unwieldy project. But from a logistical point of view alone, Whedon imposes a grip on the material that feels like that of a benevolent general, marshaling myriad technical resources (including an excellent use of 3D) while, even more impressively, juggling eight major characters, giving them all cool and important things to do.--Todd McCarthy, The Hollywood Reporter
Crucially, the wise-cracking id of Robert Downey Jnr's Iron Man is balanced out by instilling a hearty dose of fear in one of the team's central figures, thanks to a beautifully honed performance by Mark Ruffalo. He plays Bruce Banner – the brilliant scientist who turns into the uncontrollable colossus Hulk when angered – as a man afraid of himself.--Henry Barnes, The Guardian
With Earth’s Mightiest Heroes™ gathered, they needed a good villain to fight, and Loki certainly fills that void. He’s even more devious and devilish than his introduction in Thor and Hiddleston thoroughly owns the role, imbuing it with pure, malicious delight.--James White, Empire
Joss Whedon’s lavishly enjoyable, chewily-titled film (the branding’s there to warn British cinema-goers that John Steed will not be making an appearance) is an assemblage of everything that’s good about contemporary popcorn cinema; just as importantly, it’s a rejection of everything that isn’t. Avengers might be short on bright ideas of its own, but co-writer and director Whedon has a magpie’s eye for stealing other people’s, and an enviable knack of improving them.--Robbie Collin, The Telegraph
Casting's been a strength of the Marvel movies, and everyone who's returning matches their earlier engagements -- any fear that Downey Jr. might be phoning it in is misplaced, as he's actually stronger here than he was in the last "Iron Man." For the first time, Samuel L. Jackson feels engaged, rather than cashing a paycheck, and Scarlett Johansson's gone from dead weight to one of the highlights of the film (honestly, she's almost revelatory here).--Oliver Lyttelton, The Playlist
Sources: 1, 2, 3, 4, 5, 6, 7