I went back and listened to all three albums in succession to see what it was that frustrates me, and I think jonross hit the nail on the head. I love the soft, fragile vocals of the first two albums, and they often appear on this one. But when they do the operatic thing, especially on the first track... well, I don't enjoy that nearly as much. After a couple more listens I'm not quite as put off as I was at first, but it's still not as good. I love the tracks 2-4 and 8, but for me the album starts (track 1) and ends poorly (tracks 6, 7, 9). The atmospheric parts don't connect with me either.
Anyway, it's definitely a step down from the last one, but I suppose very few bands are able to maintain that level of quality throughout.