Writer-director Joss Whedon reassembles his Avengers squad—Iron Man (Robert Downey Jr.), Captain America (Chris Evans), Bruce “The Hulk” Banner (Mark Ruffalo), Thor (Chris Hemsworth), Natasha “Black Widow” Romanoff (Scarlett Johansson) and Clint “Hawkeye” Barton (Jeremy Renner)—to give December’s Star Wars: The Force Awakens a worthy box office challenge for 2015’s top spot.

The Avengers (2012) still stands tall as one of the most complete superhero movies to come from the genre’s current renaissance. As humorous as it was action-packed, The Avengers set a bar so high the Hulk, whose jumping capabilities are pretty much unparalleled, would struggle to clear it. And Avengers 2 (aka Age of Ultron) nearly clears the bar before barely tapping it with its broad shoulders.

Picking up after the fall of S.H.I.E.L.D. chronicled in Captain America: Winter Soldier and ABC’s “Agents of S.H.I.E.L.D., the Avengers still hunt for HYDRA. After toppling  Baron Strucker (Thomas Kretschmann), the super team is split by the powers of enhanced twins, Pietro and Wanda Maximoff (Aaron Taylor-Johnson and Elizabeth Olsen), leading Tony Stark to craft an über AI named Ultron. Naturally, or artificially, Ultron (v. James Spader) has other plans for peace than the ones programmed by his creator. Fortunately, the struggle leads to a pretty sweet, purple new addition named Vision (Paul Bettany).

For the most part, the second Avengers picks up right where the first left off. The banter is Whedon-ly witty. The “Buffy” mastermind really nails Ultron, and Spader wastes none of the capricious dialogue offered to him. Marvel’s comic book movies have typically suffered from lackluster villainy (see every Iron Man), save Tom Hiddleston’s Loki. Ultron is whimsically badass, as all good comic book supervillains bent on world domination/annihilation should be. Downey gets all the love, but Hemsworth may be the most underrated of the current super-actors. His charmingly arrogant Norse god gets the sequel’s MVP prize last held by the Hulk. Sadly, the angry green giant regressed in the sequel. Where The Avengers solved the Hulk conundrum, Age of Ultron returns him to grunting, inhuman form.

A sour green Hulk is a minor complaint that gets lost among the sequel’s numerous charms, but his amusing presence contributed a great deal to the first film’s rewatchability. Despite its best efforts, Avengers: Age of Ultron is not as effortlessly entertaining as its predecessor. Age of Ultron never drags but feels too weighed down by second-film-darkness syndrome, à la Empire Strikes Back. Nothing against the team’s lesser members, but several sequences involving the Hawkeye and Banner/Romanoff romantic subplots will be future fodder for bathroom breaks and fast forwarding. Even Tony Stark’s affable egomaniac routine grows tiresome, though the seeds of division sown between Iron Man and Captain America will bear great fruit in the upcoming Civil War films.

Imperfections and all, Avengers: Age of Ultron again shows how masterfully Whedon plays the notes of a summer blockbuster. Action, humor and heart aplenty, his Avengers duo is a blueprint for how to do giant superhero crossovers for the big screen. Let’s hope Zack Snyder, tasked with the upcoming Batman v. Superman behemoth, has been taking a lot of notes.