This review assumes you read the first two books in the series.
Teckla and Phoenix are book three and five respectively. I'm reviewing them both as they are linked together (whereas book four is another jump to the past).
The plot involves the Teckla (the lower class) plotting a revolution and the problems that flow from that (both for Vlad and for the Empire itself).
I was disappointed with these books, and the reason for that is that somehow the relation between Vlad and Cawti never becomes believable for me. The way they hooked up in the second book struck me as convenient to begin with and their behaviour in these books is similarly artificial.
Apart from that, it's a return to form for Steven Brust and he even goes as far as to upturn everything at the end of Phoenix (which is good, cause else the series might run the risk of becoming stale).
Weaker than the previous books, but solid enough.