“AVENGERS: AGE OF ULTRON” — ★★★★ — Robert Downey Jr., Scarlett Johansson, Chris Evans, Chris Hemsworth, Elizabeth Olsen, Mark Ruffalo, Jeremy Renner, Samuel L. Jackson; PG-13 (intense sequences of sci-fi action, violence and destruction, and for some suggestive comments); in general release

Like its predecessor, “Avengers: Age of Ultron” is an awesome spectacle, built on a foundation of well-developed characters we’ve spent years watching in previous films. It will make loads of money, and the only downside is realizing we have another three years to wait for the next one.

Based on what this film and “Furious 7” have given us so far, 2015 is going to be quite a ride.

As “Age of Ultron” opens, the Avengers are busy fighting Hydra, the villainous collective that tore S.H.I.E.L.D. apart in 2014’s “Captain America: The Winter Soldier.” We’re dropped into the middle of an operation as the full team battles to acquire the alien scepter that Thor’s brother, Loki, used to cause so many problems in the first movie.

The effort is a success, and we are introduced to a pair of “enhanced” foes: the super-fast Quicksilver (Aaron Taylor-Johnson) and his mind-warping twin sister, Scarlet Witch (Elizabeth Olsen).

One of the things that made the first “Avengers” so good was the tension between its heroic leads, and that spawns the conflict in “Age of Ultron.” After discovering some promising activity at the heart of the scepter's power, Tony “Iron Man” Stark (Robert Downey Jr.) bypasses the input of the other Avengers and uses it to create an artificial intelligence named Ultron (voiced by James Spader).

Stark hopes to fuse the AI with his Iron Legion robots to create a sentient army that will protect the planet from alien attacks like the one the Avengers fought off in New York City.

Unfortunately, Ultron’s idea of protecting the earth involves wiping humanity off the face of it. Thus, “Age of Ultron’s” heavy becomes a baffling foe, kind of like what might happen if the Internet became self-aware and decided to kill us all.

Ultron teams up with Quicksilver and Scarlet Witch, and “Age of Ultron” boils down to a good guy/bad guy faceoff. Will Ultron destroy humanity, or will the Avengers stop him first?

It’s a simple premise, but it mines ponderous themes. Ultron’s motivation is built around a desire to evolve. Though he spends most of the film operating in the form of different Terminator-like nightmare robots, he ultimately wants a biological body.

For Ultron, Spader brings his trademark high-minded intellectual sneer. It’s odd compared to what we’ve come to expect from robotic characters. But it’s perfect when you realize that Spader’s Hal 9000 with a sense of humor is nothing more than the artificial intelligence offspring of Tony Stark’s own ego.

Once again, the threat of the bad guy is offset by all the friction and distrust within the team. Stark and Captain America (Chris Evans) are having major Alpha Dog issues. Bruce Banner (Mark Ruffalo) is weighing his increasingly romantic feelings for Black Widow (Scarlett Johansson), who seems ready to reciprocate. Thor (Chris Hemsworth) is still dealing with demigod-out-of-water issues, and Hawkeye (Jeremy Renner) is wondering why he is along for the ride.

“Age of Ultron” is packed with enough wall-to-wall action and “wow” moments to entertain on their own. But like the first film, what makes the sequel work is how director Joss Whedon builds the action on this character foundation and injects it with just enough humor to make its personality radiate. It’s a very special recipe, and it is loads of fun to watch.

They may be superheroes, but the Avengers’ collective humanity becomes a major theme of the film. Early scenes have the team partying at Stark Tower, taking turns trying to heft Thor’s hammer. Later, when they need to regroup, a trip to a remote homestead turns a knowingly inferior character — Hawkeye — into the grounded human heart of the team.

Rather than feeling like a rehash, “Age of Ultron” develops and deepens the bigger narrative. But these moments never take away from the action and excitement of the film, and “Age of Ultron” is free to take its place as another triumphant stone in Marvel’s monument to summer blockbuster excellence.

“Avengers: Age of Ultron” is rated PG-13 for intense sequences of sci-fi action, violence and destruction, and for some suggestive comments; running time: 141 minutes.

Joshua Terry is a freelance writer and photojournalist who appears weekly on "The KJZZ Movie Show" and also teaches English composition for Salt Lake Community College. Find him online at facebook.com/joshterryreviews.