FF was originally bimonthly, so #2 came two months after #1. As far as we know, it's their second adventure. And yet, the story begins with the FF already famous for their super heroics, both to the general populace and would-be alien invaders - hence the Skrulls' elaborate plot to discredit them by committing crimes disguised as the FF.
As the creatures on Monster Isle in issue #1 clearly came from Marvel monster mags of the time, Skrulls are just as clearly of the ilk seen in Marvel's sci-fi comics. (Unintentional foreshadowing?) As is often the case with the early Marvel stories, it's surprising to see that from such kooky beginnings would come a race that has returned to plague the characters again and again. And check out those crazy jester collars!
This is the first time The Thing is shown to transform back into Ben Grimm. It only lasts two pages, but reminds us of the pathos of the character (especially in these early years), and the barely-contained anger and misery he constantly feels as a result; far from the gruff-but-friendly Marvel mascot he would eventually become, this early Thing is a monster, and one that the rest of the team - and the readers - expect to fly into a rage at any moment.
Goofy Silver Age writing: Reed defeats the aliens by showing their leader atrocities from Marvel monster books Strange Tales and Journey into Mystery. (Nice in-story promotion, Stan!) Not only does the leader take Reed at his word - Skrulls should never play poker, it seems - but he also apparently can't tell the difference between comic book art and photographic evidence.
At the end, Reed famously hypnotizes the remaining Skrulls into transforming into cows, then leaves them in a field. Leaving aside the question of whether Reed ever used this ability again, over twenty years later John Byrne would revisit this point in 1983's Fantastic Four Annual #17 - the very first comic book I ever bought, at eight years old - in the infamous tale of the town that grew up on Skrull milk. For a genius, Reed could sure be dumb....
Journey into Mystery #108 The X-Men #7 Tales to Astonish #60 Fantastic Four Annual #2 Tales of Suspense #58 The Avengers #8 Strange Tales #125 Amazing Spider-Man #17 Fantastic Four #31 Sgt. Fury and his Howling Commandos #10