A very strong issue
Some 1960s tales have aged badly. Others maintain their charm decades later. This is arguably a very strong issue of the series, with multiple subplots and significant changes.
Subplot #1: The fates of Magneto and Toad. Two members of the Brotherhood of Evil Mutants who were abducted by the Stranger in "X-Men" vol. 1 #11 (May, 1965). Magneto had briefly escaped in #16-18 (January-March, 1966), only to be recaptured. Here we find the two mutants living in exile in a barren planetoid. The Stranger is said to have forgotten about them, preoccupied with his new toy: the Abomination, captured in "Tales to Astonish" #91 (May, 1967).
Magneto has been frustrated by his long exile and takes out his wrath at the subservient Toad. But Max has located magnetic messages from Earth. He uses them to locate his homeplanet and teleports himself and his servant back to mother Earth. Easily taking over Garrett Castle. And setting up his next goal, the revival of the Brotherhood. Mortimer agrees, remembering their time with the group as "happy times".
Thomas successfully revives two classic Marvel villains of the early 1960s. Setting them up for a fight with Scarlet Witch and Quicksilver, representing their past coming to haunt them. John Buscema arguably draws a menacing-looking Magneto. Which arguably fits his new role as a major threat. The long-suffering Toad is depicted as a rather sympathetic figure. Rather nice issue for the both of them.
Subplot #2: The introduction of Dane Whitman, the scientist who accidentally summons the two mutants to Earth. He is the nephew and heir to the deceased Black Knight/Nathan Garrett. An extended flashback explains how his uncle got killed in combat with Iron Man. The battle took place "Tales of Suspense" #73 (January, 1966). But this the issue who establishes the fate of the Knight.
Dane is strongly motivated in redeeming his uncle's lifework. By using Garrett's technology for something of value to humanity. Redeeming their family in the process. A heroic vow. But no man is a hero to his servant. As his assistant Norris contemplates that he is doing all the hard work. A setup for turning against dane.
The heroically-motivated Dane is introduced here. He is naturally going to become the new Black Knight and a key member of the Avengers. Four decades later, the new Knight keeps redeeming the reputation of the family line. A fine addition to the cast by Thomas and Buscema. The traitorous Norris isn't going to last for long. But I like his motivation as the hired help who sees other take credit for his own work. Getting frustrated in the process. For once, a human" villain" with very human motivation.
Subplot #3: Captain America quits from service with the Avengers. Explaining his motivation for the act. "Because it's time that Captain America died -- so that Steve Rogers can finally live again! Isn't that reason enough?" He wants to establish his own life in this new era. Something he hasn't been able to do since reviving in issue #4 (March, 1964).
Hawkeye is quick to accuse him of breaking their oath. What oath? Back in #16 (May, 1965), they all swore to continue the Avengers' tradition in the way the founders (Giant-Man, Iron Man, Thor, Wasp) had intended. Cap points that he has fulfilled his personal oath. Which was to hold the team together, until the original Avengers returned to take over. No that Hank Pym has returned, he can have the obligation of keeping this team going.
A very human moment for Steve Rogers. Because he wants to have a life of his own. Not just be Captain America and an Avenger. He wants to be Steve again. Nice. The decision of this issue did have lasting effects. While Cap will team-up with the Avengers again, he stays off the active roster until #93 (November, 1971).
Subplot #4: Hawkeye feels frustrated at Cap simply leaving like that. A date with Natasha (the retired Black Widow) goes poorly. Clint at first ignores her. Then shouts about having "other things to think about", not just her. He quickly realizes that its not her fault. But storms out instead of apologizing.
Natasha seems about to cry. She feels that quitting her career as a superhero was a mistake. Now heroics in general and the Avengers in particular are parts of his life that she can't share. She also wonders something else: "Does he really love a girl named Natasha ... or only the Black Widow?"
Clint has his own human moments. Feeling frustrated about problems and taking it out on a loved one. The self-doubt of Natasha is endearing. This already sets the stage for her return to the Black Widow identity in #57 (October, 1968). I kind of like the heroes having this very unheroic-moments. Makes them more relatable.
Subplot #5: Hank Pym is feeling depressed. Wasp tries to cheer him up with a vacation to Las Vegas, Nevada. They are driven to the airport by their loyal driver Charles (actually the Whirlwind).
This one scene we are going to see many times ahead. Hank depresses, sour-faced, frustrated. Janet trying to cheer him up and have him live a little. A couple with rather opposite attitudes towards life. Their dysfunctional relationship is always interesting. Their archenemy being in their employee is both amusing and a bit creepy.
Subplot #6: Hercules flies to Greece. He has finally found the courage to perform an unfinished task which. He climbs Mount Olympus to confront Zeus and reclaim his position among the Olympians. He wants to live on Earth. But he wants it to be his choice, not a sentence of exile.
He is in for a very nasty surprise. The homes of the Olympians still stand, alongside monuments "to glories past". But not a single person lives there. All his "fellow immortals" have mysteriously vanished. A miserable Hercules vows to learned what happened to them, even if it takes him "all eternity" to do so.
Some growth for the resident immortal. First having the stones to go confront his father. Then left with a decision to learn what has happened to his family. This is a set-up for issues #49-50 (February-March, 1968) and the introduction of Typhon. But I liked seeing the serious side of the party animal.
Subplot #7: Magneto explains his personal connection to Wanda and Pietro. "X-Men" vol. 1 #4 (March, 1964) already gave a brief origin for them. Told in two panels and having Max saving Wanda from a couple of superstitious peasant. Here Thomas and Buscema expand the scene to three pages and add more details.
Wanda accidentally set several houses on fire with her hexes. The villagers attacked both siblings to lynch them. Pietro fought them for a while. Only to become overwhelmed and end knocked out. The mob was ready to kill them both in rather painful ways. When Magneto arrives and easily disarms the whole village. The villagers perceive him as "Satan himself" and flee for their lives. From then on the siblings were bound to him by a debt of honor.
The relatively insignificant scene from the annals of the X-Men becomes an epic battle in the pages of the Avengers. Bravo! A critical moment for all three characters involved. Also used to explain why Magneto feels connected to these two. Willing to let Mastermind go on his own way for the time being. Nice to know that it is a personal matter for him.
Subplot #8: Magneto lures his former proteges to Garrett Castle, eager to test their powers in battle. They have no idea who they are facing, simply confronting a robot. Pietro easily evades its attacks, while Wanda destroys it. But they are then confronted by Magneto himself and an entire army of robots.