My 2 cents after a couple of listens is that I like it a lot more than most here seem to.
It definitely moves slow, but not so slow as to bog down, I think. Though, I understand pretty much all of the criticism too. It is long, and plods along, broadly speaking, at about the same pace throughout, giving one less variety than might be necessary in such a long undertaking.
Still, most of the songs are pretty good, taken alone, and some are fantastic (Persecution, Death, Exiled, a few others).
My thumb is more up than down on this one, with an extra half star since I thought it was gonna suck from the get go, that is, as soon as I heard it was a concept album about Nostradamus I thought...uh oh. They could have chosen a more "metal" and obscure figure, like John Dee (16th century occult figure), or even Crowley, but oh well. Nostradamus is about as interesting and metal as an afterschool special.
Still, it does have an older Priest vibe to it in its darkness and lack of huge choruses. It's not old Priest in any way, I just mean the overall vibe is more similar to 70s Priest than it is post-70s. Again, not in quality or even style, but in vibe. That's cool. However, the one obvious ballad is really pretty bad (Lost Love).
It's pretty good overall, I think. I can see why Wyvern (and others) don't like it though, as it is a rough equivelent of the new Maiden stuff, which I know doesn't sit well with you either. I think old Maiden fans who embraced A Matter of Life and Death are more likely to embrace this (if they are also old Priest fans).
It'll be interesting to see what new fans think.
If nothing else, and I really do think its pretty good, at least they tried something new. They get points just for being willing to explore this late in the day, as it were.