Fantastic Four #5
This is the first appearance of Dr. Doom in the Fantastic Four. The plot is goofy (although that's to be expected), as Doom sends the three of the Four back in time to capture Blackbeard's jewels, which were supposedly enchanted by Merlin (or something).
Again Susan Storm plays the damsel in distress. Are there any feminist comics blogs out there? I'd be interested in reading feminist interpretations of these early silver age issues. The degree of sexism in these Silver Age comics is laughable, even for that era of American culture. I liked this story overall, though, especially the twist where it turns out that Thing is actually Blackbeard. The time travel stuff makes no sense, but time travel fiction never does.
A lot of people have written about how the interaction between the members of the Fantastic Four made these issues unique compared to other superhero comics of the era, but I think the villains from these early issues were pretty solid. In the first five Fantastic Four issues, we have key appearances from the Skrulls, Namor and Dr. Doom, all of whom went on to some level of popularity in Marvel comics.
With that being said, these early issues of Fantastic Four are definitely for serious fans only, as you really need a child's imagination or fervent dedication to the Marvel universe to enjoy these.