As @Miqque noted, this cover, and the opening flashback are rendered in the style of Jim Steranko's Nick Fury comics from the 60s. And as @Chris noted, that's Dum-Dum Duggan getting shot in the first panel of the book. And Bride is reminiscent of Madame Hydra.
Keeping up the gadget-strewn superspy thing, Stone gets in a post-mortem quip after he immolates some of Bride's "children". This being Planetary, their deaths are rather gruesome to highlight just how sociopathic those quips can be,
There's also a line of dialogue that suggests Stone knows Anna Hark,
There's a few more WSU references going on here, with Stone calling for backup from STORM Watch, and the Last Shot bar from Ellis' run on Stormwatch showing up. Also, this might be the last we see of connections to the WSU in Planetary. It increasingly becomes its own thing from here on out.
The twist in the 1969 chunk of the issue is that while we'd usually get a story to which Planetary are observers after the fact, here Snow was actually there, and was integral in saving Stone's life. This is a significant change which indicates that this issue is the point where the dominoes begin to fall, and Planetary begins the shift to the second half of the story.
And so we move to the year 2000, and Stone and Snow meet up at the Last Shot, and we learn quite quickly that Snow and William Leather clashed as early as 1959 - two years before the Artemis mission. And Stone then sets about answering the one of the questions Leather asked Snow at the end of book 1.
Who benefits from Snow's lack of memory? The Four do.
But as always, that answer leads to more questions - why would the Four not just kill Planetary? In Dowling's own words: It's a game.
A couple of months ago, Stone met someone with a Planetary Guide from 1931.
And then the floodgates open. We see snippets of Snow exploring, fighting, loving, learning. This is not the man we've come to know over the last book and a half - we've seen a curmudgeon, a man who's fascinated by the world but also tired. A man who's been hiding away in the desert with only a shit diner with a bitchy waitress for company, and was happy with that for the longest time. The Snow we see across these two pages is vibrant and exciting, throwing himself into danger.
And the Snow we see on those last two pages is different again. He's shrewd,he instantly grabs onto Stone saying he was doing consultant work for the Hark Corporation earlier in the issue - which Stone acknowledges as Snow being 'back to normal'.
And this new old Elijah Snow knows who the Fourth Man is.