I love Maiden, but I was never huge on TNOTB. It's a great album, and I get the classic status, because it has Maiden's two biggest hit songs on it, as well as being the first album with Bruce on vocals, but overall it's not one of their best for me. Funny enough it's mainly due to the hit songs that I don't care for it, Run to the Hills have always been one of the weaker Maiden songs for me. I totally get why it's a hit and why other people like it, but I guess it's the case of being overplayed. Still, Hallowed Be thy Name, Children of the Damned, The Prisoner and Invaders makes this a really nice album.
I'd say it's a 8 out of 10 or so. Maiden has done much better albums (Powerslave, Seventh Son, A Matter of Life and Death among others) but it's still a very solid middle album.