It's the conclusion of the first two-parter in "What If..." and boy is it a doozy. This episode is a culmination of everything we have seen this season. Infinite Ultron presents a threat to the entire multiverse, but he's not the only one. When we left off last week, the Watcher decided to break his oath. Now we pick up with the consequences of that decision.
Watcher. Comics fans will remember Uatu, a member of the race of Watchers, immortal beings of great power whose duty is to observe events, but never intervenes. In this episode, however, The Watcher not only observes events but finds himself participating when Ultron threatens the existence of every universe. The Watcher becomes a character rather than simply a narrator, and must decide whether or not to violate his Prime Directive.
usually mean is that a lot of MCU villains are poorly developed, flat, and not very sympathetic. Malekith is probably the most egregious example, but you could include Kaecilius or Whiplash. But sometimes the MCU absolutely nails a villain. That is definitely the case in Black Panther. Killmonger is deeply troubled and carries a traumatized past. His plan was terrifying, but sympathetic too. So it only makes sense that they would bring one of the MCU's most fascinating villains back for a trip through the multiverse.
There are a few classic horror monsters that have been around so long that it can sometimes be hard to do in a new an interesting way. Sure, I guess you can make your vampires pretty and sparkly, or make Michael J. Fox your werewolf, but zombies have been around in film so long that it's hard to make them new. Even "The Walking Dead" got boring by Season Five and anyone who tells you otherwise is deluding themselves. But wait a second, this is the MCU, and we're experimenting with alternate timelines. That means our zombies could use weapons, like the Iron Man suit, or magic and superpowers. Holy crap, that means this week we are asking: "What if... zombies!?"
"Absolute power corrupts absolutely", or so the saying goes. Our favorite nerdy fictions are full of examples of truly good characters who wielded power far beyond anyone else in their world, but refused to use that power selfishly. I'm thinking of Charles Xavier's reluctance to read minds without permission, Gandalf's refusal to touch the one Ring, and Dumbledore's decision to avoid politics and settle into a quiet career in school administration, since everyone knows that schools are never, ever political.