Jan being the best pianist in the world (Situational Irony)
It is ironic that "Jan had always been a good pianist--and now he was the best in the world," because, of course, he is the only human being left at that point in the story (203).
Narration of the world's end (Situational Irony)
As Jan himself observes, his narration of the end of the world is ironically done: "Here was the climax of all hsitory, yet he might have been a radio-commentator at the race-track or a boxing ring" (208).
The nature of the Overlords (Dramatic Irony)
It is ironic that the Overlords look like devils when they are more akin to Guardian Angels. It is also ironic within the overall genre of science fiction that these "invaders" are actually benevolent and bring about positive changes to humanity rather than destroying it.
The inferiority of the Overlords to humans (Dramatic Irony)
It is ironic that the Overlords, assumed to be far superior to human beings, are actually an evolutionary dead-end and envy humans for being able to transcend their current state.