The original 2012 "Avengers" (which featured the rarest of superhero movie insults: "mewling quim") should have had more of them, and there's even less room in the massive — and massively overstuffed — "Age of Ultron" for Whedon's dry, self-referential wit. [...] it instead pushes further into emotionality and complexity, adding up to a full but not particularly satisfying meal of franchise building, and leaving only a bread-crumb trail of Whedon's banter to follow through the rubble. The action starts predictably with the Avengers, now assembled, assaulting a remote HYDRA base in the fictional, vaguely Eastern European snowy republic of Sokovia. Robert Downey Jr.'s Iron Man, Chris Hemsworth's Thor, Mark Ruffalo's Hulk, Chris Evans's Captain America, Scarlett Johansson's Black Widow and Jeremy Renner's Hawkeye. [...] the dive into the vulnerability of the Avengers doesn't add much depth (is the home life of an arrow slinger named Hawkeye important?) and saps the film's zip. The movie's hefty machinery — the action sequences, the sequel baiting — suck up much of the movie's oxygen, and the mammoth action scenes have a way of crushing the smaller moments. In the relentless march forward of the Marvel juggernaut (the next "Avengers" movies are slated for 2018 and 2019), "Age of Ultron" feels like a movie trying to stay light on its feet but gets swallowed up by a larger power: Age of Ultron, a Walt Disney release, is rated PG-13 by the Motion Picture Association of America for intense sequences of sci-fi action, violence and destruction.