How do you mean it is poorly mixed? I think it's better mixed than both Dance of Death and A Matter of Life and Death, which I think lacks in bottom end and Nostradamus has got lots of it. Opinions varie though.
About Halford "not sounding that great", are you talking about him doing less screams? I tell you, I don't think (I say think because I'm not Halford therefore I cannot possibly know for sure) it is because he's older. Falsetto screams aren't that hard to do, he's pulled off quite a few good one's lately on tour and he's gone pretty high WITHOUT going into falsetto (some recordings of the chorus in Devil's Child testifies that excellent.) and the falsetto screams on Metal Gods and Between the Hammer and Anvil are excellent, so don't tell me he can't do it ( however, I'll give you that he can't sing Painkiller live as he used to. Perhaps he's able to in the studio, but I don't know).
Check the titletrack too. The high notes in the line He's avenged" aren't falsettonotes either, it is just about the highest part of his head voice. I can't go quite as high in head voice and still sound good. My voice breaks. Then again, I'm not a good singer.
I will, however, give you that Priest's lyrics aren't exactly poetry. I'll also add that taste is all that matters. If you don't like it, you don't like it.