Not really sure what to think, I really liked the previous reunion-albums (BNW, DoD and AMoLaD), but The Final Frontier was kinda meh.
First half of the album was rather mediocre, second half had some gems (Starblind and Isle of Avalon especially), and the second half of the album was really what saved it from being very low in the Maiden-discography.
One thing I'm a bit skeptical or thinking about at least, is the more up tempo/faster songs.
Personally I don't think they've made that many of them that I've liked in the last ~3-4 albums, and I think their best songs (also most memorable) has been more epic & long songs, Paschendale, Dance of Death, The Legacy and Starblind are a few that comes to mind.