I tend to be of the opinion that nearly every album, by any band, has a song which I don't like. With regard to Iron Maiden, this is not always true. But anyway, for the first album, I have to say that I really dislike Strange World. I love the Killers album and can only express a mild dislike for Prodigal Son, and the same goes for Quest for Fire on PoM. Fast forwarding to the No Prayer album, it would be Public Enema #1, while there are a few on Fear of the Dark that i don't think are particularly good.
As for the X-Factor, it is very low on my list, and in listening to the two most recent albums, Brave New World and Dance of Death, I'm happy to see that the band have got past their midlife crises (confirmed in the "Run to the Hills" book) and are ready to continue with making heavy metal music. Lines like "Should we be fighting at all" sound prosaic, in my opinion. "Como Estais Amigos" is, possibly, my choice for absolute worst song by the band, ever.
The only problem i have with the song "Dance of Death" is the use of one word. The word "pranced" does not belong in an Iron Maiden song, or, frankly, in any heavy metal song.
Despite my opinions, I'm glad to see that there are plenty of people who are fond the songs I disliked. I've been very surprised to see how many Iron Maiden fans like the X-Factor album. I have to admit that the songs sounded great when I heard them live in '97. On the other hand, I am also surprised at the amount of fans that dislike "The Fallen Angel". To me, it is a true rocker, fast and furious.