A street brawl
This issue is considered a milestone for comic books in the Silver Age. For one thing it features the second superhero wedding in history. Reed Richards and Susan Storm finally get married. There were few married superheroes before and their marriages mostly occured off-panel. The one major exception being the wedding of Aquaman and Mera in "Aquaman" vol. 1 #18 (November, 1964). For another thing this Annual features the greatest gathering of Marvel characters by this point. Not to mention a chance to see characters switching opponents for once, long before "Acts of Vengeance" further explored this idea.
Those are all significant points. But the issue has a couple of major flaws. First, this is not exactly a masterful plot. When Dr. Doom sets out to "Fan the flames of hatred in the heart of every evil menace in existence", one would expect to see some of the greatest criminal masterminds of Marvel develop cunning plans. Instead the issue pretty much covers one extensive street brawl where pretty much anyone engages random opponents. No sense of strategy here.
This could be overlooked if not for the other major flaw of the issue. There is no real focus on any aspect of the battle. We hardly glimpse what any single character is really up to. For example, Thor and Super-Skrull are supposed to spend most of the issue fighting each other to a standstill. But only a hand full of panels deal with this battle. Even worse, a high-speed battle between Quicksilver and the Human Top (Whirlwind) is resolved in only two panels.
At least there are several amusing scenes here. For example, the Red Ghost and the Super-Apes give a decent battle to the FF. Then Dr. Strange exiles them to another dimension within a single panel. Pointing just how powerful Stephen is. In the most over-the-top subplot of the issue, an armored truck of HYDRA transports an enormous "Vortex Bomb" to the Baxter Building. Daredevil hijacks and drives the truck straight to the harbor. Where the bomb explodes and thwarts a full-scale invasion by Attuma! I had to laugh out loud at the only blind superhero present both doing the driving and ending the two greatest threats of the issue.
The issue ends with Uatu acting as a "deus ex machina" (Latin:god out of the machine): " a plot device whereby a seemingly inextricable problem is suddenly and abruptly solved with the contrived and unexpected intervention of some new character, ability, or object." Uatu basically teleports Reed straight to a powerful device in his possession. Reed then uses said device to send the various villains to the recent past, prior to the battle. With them loosing any memory of the battle in the process. Uatu argues that he wasn't technically interfering.
Yeah right. Though a somewhat annoying resolution to the escalating battle, this paves the way for several more times of Uatu bending the Watcher rules. Too bad we never really see this wonderful device again.