I have tried to summarise my biggest complaints regarding Empire and I think I have it.
1. It's way too melodramatic. You would have thought he's singing about the fall of Babylon or whatever.
2. However, surprisingly, it also (musically) lacks a clear climax - it just ... is. And then it isn't.
3. The instrumental part could have been longer and better. Also, no Janick solo.
4. Along with the previous - for 18 minutes it's way too repetitive and simplistic. Not enough meat on these bones.
5. Also, it's way too vocally, lyrically and atmospherically driven for its length.
6. The SOS is a cool idea in theory, but it brings the song to a halt... more than once. It also sounds very jarring, like a cut-and-paste songrwriting.
7. I don't like what Bruce is doing there - the first six minutes sound more like Hammill/Gabriel/Waters, heck, Bowie even, than Bruce and Maiden.
8. And finally... I just don't see this as Maiden, full stop. It would be great on a Bruce's solo album, mabe even on a special Maiden EP (like DT's A Change of Seasons), but it just doesn't fit the TBoS album, IMHO. It should be separated from the rest of their work, because it's not that much about the band, it sticks out like a sore thumb and it's way too weird to compare it with the rest of the Maiden material.
Also this:
It really comes off more as a folk song than a prog rock epic
Mosh has put it perfectly.
That said, I still like it. But I usually listen to it separately from the rest of the album and I don't get the adoration it gets.