On the question of the quality of 'The Final Frontier', I have a foot in both camps. On the first few listens, I honestly wasn't that struck on it but part of that is because I think it was the result of Adrian pushing the boundaries again. I think it all worked a lot better live. It has since grown on me a bit more and I suspect it will continue to do so. What I dislike most about it is Bruce's vocals which sound painfully strained at times.
The Final Frontier was definitely an album that took some getting used to, needed a few listens to really get into (especially the second half of the album). I think WTWWB and Coming Home were the only two songs that jumped out right from the word go. Since then both of them have sunk a bit, especially Coming Home. I really most agree with you on the Bruce voice issue, I don't understand why they thought it wasn't abrasive to have Bruce sound so strained (I'm thinking of The Talisman in particular). After all the hoopla and hype over The Final Frontier has died down, I expect only Isle of Avalon, Starblind, The Man Who Would Be King, and When the Wild Wind Blows will stick.
This then goes back to something else we've begun to discuss here, which is how each one of us is biased towards certain albums or era's based on when we got into Maiden. I make no secret that I have a soft spot for Brave New World because that was the first full studio album I owned and heard in its entirety (and also has the first ever Maiden song I heard which was Blood Brothers). The same thing goes for Death on the Road as that was my first live album and actually the first Maiden album I bought. But I think that as long as I'm aware of this (that I have this nostalgic bias) it's all ok. It doesn't prevent me from making open-minded, receptive, judgements about other albums. Its not like BNW constitutes the highest bar for Iron Maiden, its simply an album that I enjoy very much. Other albums, such as Number of the Beast, I heard much later and took a long time for me to like. I remember I used to really hate Invaders and I still think its the weakest song off that album, but its not quite so horrible-sounding anymore somehow.
But I did start listening to Maiden in the 00's and so its very likely that I have a bias towards this newer era of Maiden. If I were to try and get a friend into Maiden, the songs I'd supply would lean heavily towards their newer stuff, with a few classics mixed in. Legitimately I'm not sure if this has to do with the sound quality, the direction Maiden have taken, my bias, or a combination of all of the above. As someone coming from a classical background I do definitely prefer the more intricate, longer, orchestral-leaning, melodic (even if its repetitive), works.
To close, I think liking Iron Maiden is a very amorphous, dynamic, pulsing, thing. Things I used to love 5 years ago may have fallen off the radar and things I wouldn't have given the time of day have come to the foreground. A good example is AMOLAD, which I loved when it came out in 2006 but has since dropped in listens, and has now re-emerged. Its strangely almost as if Maiden lives and grows and breathes with each one of us, molding itself to each of our life journeys. Thats the magic of Maiden I think. Perhaps its the "Maiden sound" or something more intangible than that. Whatever it is, it lives and dies by Steve Harris' vision and in my opinion comes to full fruition in the current line-up.
The difference is that I loved the first album. I think it was because I was really into Punk at the time and that first album has quite a Punky feel to it, except Maiden can really play their instruments!