This, the sixth and last installment in the series, suffers from the same problems as the fifth book, and suffers from them in spades. It's very disappointing that such a good series should deteriorate like this. The politicking is still there (although perhaps not as much as the previous volume) but the silliness, culminating in nuclear carpet-bombing, is just so ridiculously over the top as to offend my sensibilities, even allowing for the fact that it's fiction and for dramatic suspension of disbelief.
I almost gave this just one star but it's just about pulled up to two by the fact that it's pretty much required reading if you've already got this far - just be prepared to be disappointed, even if you weren't disappointed (and you should have been) by the previous installment.
The end is somewhat intriguing and sets up more potential sequels, which may be improved by having had the obnoxious feudalism killed off along with all its incomprehensible politicking. There's a few interesting directions in which it could go, depending on which of the loose ends Stross decides to follow up on, if at all - on his blog he says "I'm not ruling out writing more books in that universe â" but I'm taking a couple of years of time out first, and if and when go back to there, it'll be with a new story and mostly new characters". Good, it could do with a partial reboot.