The rocky, but enduring, relationship between Tony Stark and Steve Rogers is at the heart of “Avengers: Endgame,” a bloated onslaught that effectively delivers on its billion dollar promise.

“Avengers: Endgame” brings to a close phase three of the Marvel Cinematic Universe, even though studio heads don’t want you to forget about the July release of “Spider-Man: Far from Home.” “Endgame” is an amply stuffed present for devoted fans who endorsed and supported the brand since 2008’s “Iron Man” kicked off the new comic book movie era. And while the film has plenty of battle sequences and familiar superhero feats, the remarkable thing is how dramatic the quiet moments prove to be. There’s more high drama at work in this team-up feature than anything in the series. But the soft and tender moments work best.

The complex bromance between the MCU’s two biggest heroes is critical.

The manipulative, almost to the extreme, narrative, based on comic book characters filtered through Hollywood’s lens relying on varying director visions and personalities, capably pieces together the whole of the Marvel Cinematic Universe. This adventure finds the survivors from 2018’s “Infinity War” grappling with the consequences of Thanos’ crippling decision. What took but a snap of the finger, could, conceivably, be reset with another snap. And with half the universe’s population instantly reduced to ash, it’s easy to get depressed.

At one point, Steve Rogers aka Captain America (Chris Evans) leads a group therapy session where he draws on his time in the ice in order to encourage folks to move on. But, of course, no one can, especially, the remaining Avengers.

Black Widow and Hawkeye mourn their losses.

So, led by Black Widow (Scarlett Johansson), the Avengers search the stars and the heavens for Thanos in hopes of capturing the powerful Infinity stones and reversing his murderous deeds. But if they do get the stones, can they bring everyone back? Should they even try? These and other weighty questions hang over “Avengers: Endgame” as the heroes debate the right path to take. Oh, and there’s more than a few references to “Back to the Future.”

Given our affinity for the now iconic screen heroes, namely Iron Man (Robert Downey, Jr.) and Captain America, it is easy to get emotionally connected to the character’s fate. For the record, and not spoiling anything that isn’t already revealed in the trailers, Cap and Iron Man survived Thanos’ decision. But because they are heroes, who solve problems, the Thanos question is one they endeavor to answer. But some of the team are intent on moving on. Tony Stark starts a family, and Bruce Banner (Mark Ruffalo) has spent his time productively studying gamma rays.

Everyone grieves in “Endgame.”

Of course, the old chestnut that with great power comes great responsibility leads the crew to try to make things right, none-the-less. And this naturally leads to a series of exciting action sequences that incorporate a little bit of every character that has previously graced the screen in the massive franchise. It’s a cup that nearly runneth over.

The mysterious missing confound the Earth’s remaining inhabitants.

Without any apology, no character is left without a role in “Endgame.” This understandably makes for an overstuffed and busy movie that, at times, feels like a laundry list being checked off. Regardless, fans will cheer with each character’s appearance, no matter how brief. And at right over three hours in length, co-directors Anthony and Joe Russo still manage to inject a measure of humor and pathos into a ridiculous story that will have some viewers in puddles. Thor (Chris Hemsworth), in particular, is given time to emote, as the loss to Thanos (voiced by Josh Brolin) sends him on a drunken bender that literally turns the God of Thunder into a completely different guy. I wouldn’t dare spoil his appearance, but his scenes are something of a show-stopper.

Epic in its sweep and intent on covering all the bases, “Avengers: Endgame” is fan service on steroids. And that’s not such a bad thing.