This episode has got to be one of the best, if not the best episode so far. Everything that happens in it will impress you and leave you wanting more. The threat that has been mentioned or present in the last two and a half seasons, the Apocalypse, is here.
The beginning is great, as the X-Men capture Mesmero and force him to say what Apocalypse plans to do. They are shocked to learn that Apocalypse plans to turn the entire world into mutants. Most of the humans probably won't survive the process. Xavier decides to travel to Egypt and reason with Apocalypse. He insists on going alone, but Storm comes as well. They arrive in Egypt, where they find Apocalypse has evolved, and his new impressive design really inspires fear. He seems more powerful, no more the weakling we have seen so far. And last but not least, he finally speaks, and his voice-actor does a great job.
Xavier tries to reason with him, but Apocalypse won't listen. He merely waves his hand in the air and Xavier explodes in front of him (similar to how Magneto was destroyed in the season premiere, also by Apocalypse). Storm attacks, determined to avenge Xavier's death, but she too is destroyed by Apocalypse.
At the Institute, the X-Men watch in terror what just happened and are shocked by Apocalypse's powers. Jean leaves the room crying, realizing that Xavier knew this would happen to him all along, but he still went. Cyclops tries to comfort her, and we get another one of those rare Jean/Scott moments.
Wolverine decides it's time to attack before it's too late, and sends the others to gather as much help as they can. Nick Fury returns in this episode, introducing the new and improved Sentinels, now capable of fighting only Apocalypse. The plan is to destroy the energy spheres Apocalypse has created to protect his pyramids, and then enter them to destroy everything they find. Wolverine reluctantly agrees and accepts Fury's help.
The teams are formed, and each one leaves for a certain destination. Apocalypse senses his spheres are under attack and creates his Four Horsemen, and the scene is amazing, as well as the background music used. Who are his Horsemen? None other than Xavier, Storm, Magneto and Mystique (how exactly did Mystique get there I'm not sure, but it adds a lot of emotion to the story).
The final fight is about to begin, and after an introduction like this, the story can only get better.