Their second LP, 1981's "Killers", is an extraordinary LP with no weak moments and several that are simply transcendent. "Killers" finds them settling into their classic sound: guitarist Dennis Stratton was replaced by Adrian Smith, who combined with Dave Murray to solidify the "Iron Maiden dual harmony" sound that would define their career. In addition, "Killers" was the first LP to have their long-time producer, Martin Birch, which resulted in a slightly fuller if muddier and heavier sound than their first LP.
As I said in my review of "Iron Maiden", I enjoy the first two LPs without the crutch of nostalgia or a hint of irony (cf. my recent review of "Too Fast for Love"). They were right to fire Di'Anno in late 1981: he was a troubled addict, and Iron Maiden would never have become "Iron Maiden" had he stayed at the helm. But the first two Iron Maiden LPs are special.
Standout songs: "Ides of March / Wrathchild", "Murders in the Rue Morgue", "Killers", "Prodigal Son", "Purgatory" (Full LP)
Skip 'em songs: none.
Final rating: 10/10. A NWOBHM masterpiece.
Bonus link: my review of "Live at the Rainbow", a 1980 concert with Paul Di'Anno.