There is no such thing as a bad Maiden album and I can find of plenty of good things to say about all of them, but I think that they really play to their strengths more with these three.
For AMOLAD, they took the wild experimentation of the last record Dance of Death and refined all of it. That album stepped it up when it came to longer songs, but on AMOLAD the longer songs comprise the majority of the tracklist, so they really needed to make them strong, and they succeeded. The writing and topics became more focused, being entirely about religion and war instead of the myriad of topics covered in Dance of Death. It's also their heaviest album which doesn't mean much in the grand scheme of Iron Maiden's music, but hey it's something. I don't think the band ever sounded more pissed off than they do in songs like Brighter than a Thousand Suns or The Legacy.
The Final Frontier is somehow even more cohesive thematically than AMOLAD and still engages in experimentation that far into the band's career. At the same time, the sound is more accessible and modern. It's definitely their proggiest release to date and the band tries to give every song a spacey feel. While the epics are around the same level as the previous album, I find that the non-epic songs are slightly more enjoyable than the ones on the previous album. The flow is extremely tight, with most of the longer songs saved for the back half. You get the atmospheric and somewhat cryptic Isle of Avalon, followed by the crystal-clear clarity of Starblind, then the very intense Talisman followed by the calmer and reflective TMWWBK. Finally, When the Wild Wind Blows is a deceptively deep cautionary tale. That's another thing I wanted to mention, the lyrics really took a step up on this album and on AMOLAD.
Senjutsu is in my honest opinion the best album Iron Maiden ever created. While many would decry that The Book of Souls and Senjutsu are derivative, I would say that Senjutsu is the band having full faith and assurance in their sound. The Iron Maiden formula is so good because of how distinct it is, and how adaptable it is to any time or theme. While The Book of Souls contained a few songs that felt like tributes to the band's past work, Senjutsu extracts the vital essence of the past and directs it to something new. In other words, they are relying on what works while still trying new things. This album is Iron Maiden on steroids since they took their epic songwriting to the next level on here. Songs like Death of the Celts and The Parchment are less like campfire stories and more like epic poems passed down through generations or perhaps lost to time. There is a real sense of urgency and experience to this album, and you can sense this from track 1. There are also motifs musically and lyrically that pop up all throughout.
If you are not a fan of these, that is okay. I just wanted to explain why I like them so much and to see if there was anyone else who thinks the same.