I personally think CoG lived up to expectations. I can understand that Cassandra Clare couldn't put a lot of the witty banter that Jace and Clary had in the first 2 books because the circumstances are more serious in the third book. If there's a war on, you tend to be more morose. But I think the other characters more than made up for it. Magnus, Alec and Simon provided a lot of hilarious breaks.
I loved the deeper characterizations of Luke, Jocelyn and Valentine in this book.
The blogs showed that there's a fourth book called City of Fallen Angels. It will be about Simon. Another good thing to look forward to!