Well, I think to some degree, you had to be there. It might be "overrated" in the sense that any ONE album that is used to classify an entire band is "overrated". Machine Head. Pyromania.
But as someone who was getting into metal at that time, and had "High And Dry", and had "Maiden Japan", and "British Steel" and "Point of Entry" (which were much more... 70's), then you got "Run for your li-I-ife!" in that soaring, operatic way - something that Di'Anno just simply could not do - it was something new. Then the epic-ness of "Woe to you oh earth and sea... for the devil sends the beast with wrath, because he knows the time is short. Let him who hath understanding reckon the number of the beast..." then that scream... It changed the game.
..and this will sound like "you had to be there" but I prefer to use the term "Listening in real time".
I mean, it's easy to pick any band you are new to and line up all of their albums next to each other and pick a fave. So, if you put TNOTB next to AMOLAD, I can see why some would choose AMOLAD.
BUT...when TNOTB came out, it truly separated them from the entire NWOBHM movement. It was fresh and exciting. It was the kind of music that no one else was making, and it was both progressive (I use the term progressive to mean that it pushes a boundry of their original genre) and accessible.
For all of the glory of the NWOBHM, it produced TWO bands: Iron Maiden and Def Leppard. Sure many other bands did OK, and Saxon, while enjoying a great renaissance over the last decade, were nothing but second class citizens once Maiden and Def Lep hit it big. Both took Saxon's (and Judas Priest's) template and progressed it. Def Lep took it to a Pop direction, and Maiden took it to an arena style, epic direction.
TNOTB separated Maiden from the pack on musicianship, song writing, and performance. It made an impact and impression, that cannot be clearly seen by looking back through time. It could be argued that they refined their craft a bit on Piece Of Mind. Sure.
Kind of like Images And Words and Awake. Both albums did the same for Dream Theater as TNOTB and POM did for Maiden.
Oh, and 22 Acacia Avenue is a TAC Top 10 Maiden track!