This a pivotal issue of The Avengers for a number of reasons.
First The Avengers #72 marks the initial time that Captain Marvel then in his "Silvertop"-period Negative Zone-relationship with Avengers "mascot" Rick Jones met up with the Avengers team. Cap's own series had been put on hiatus the previous month. This 1970 meeting would be critical a few years later when Mar-Vell and Rick again hooked up with the Assemblers to help wage the Kree-Skrull War.
Second, the issue gives some resolution to a mystery left hanging with the demise of the first SHIELD series, the seeming death of Nick Fury himself at the hands of the first Bulls-eye.
Also the mystery about what was the relationship exactly between Nick Fury and his arch nemesis Scorpio was uncovered. We learn in this issue that Scorpio was in fact Nick's brother Jake.
As part of that reveal we also meet for the first time The Zodiac, who have since become arch enemies of the Avengers and others. I was truly excited by the double page reveal of this colorful (if admittedly sometimes goofy) gang of baddies. Marvel made sometimes great and sadly sometimes poor use of them in the years to come.
But a third thing always stands out about this issue drawn by Sal Buscema and inked by Sam Grainger. This was not the first issue to feature the Avengers conference table with the big honkin' "A", that might've been The Avengers#34.
But it was the first to my memory to show all those ginchy specially designed chairs for every member with the nifty hero-specific symbols on the back of each.
Can you imagine how frustrating it got for Jarvis and his maintenance crew to keep changing out Hank Pym's chair as he morphed his identity over and over. There must've been a closet or shed somewhere with a bunch of Hank's old Avengers chairs in it, just waiting for the next permutation. Clint Barton must've given them the shakes too.
I wonder if these chairs are Sal's own invention, or a detail of Grainger's inking, or were perhaps indicated in the script by Roy Thomas. This is the kind of earth-shaking continuity info that once upon a time might've inspired Roy or a late Mark Gruenwald to write a complete story.
Whatever the case, they sure came a long way since those early days when they were sitting on milking stools.