The original intended finishing installment of The Mortal Instruments, 'City of Glass' reads like the finishing volume of a bigger story but unfortunately all the problems of the previous two books continued plague Cassandra Clare's story.
The book revolves around Valentine's endgame by attacking the Shadowhunter capital of Alicante in the hidden country of Idris, which Clary and the reader see for the first time. The overall plot reads well, however the twists and turns along with the character interactions were more often than not just bad. The relationship between Jace and Clary did resolve itself in the predictable fashion thanks to a surprising new secondary antagonist allied with Valentine along with Jocelyn waking up and talking with Clary. The antagonist relationship for most of the book between the Clave and the Downworlders given what happened during Valentine's previous coup attempt was one of two big plot holes, the second was the sudden disappearance of the other surviving Shadowhunters from Valentine's boat in the previous book which affected a major secondary character's story arc.
I would be remiss if I didn't point out things that were well done, the first of which was the character of Simon who kept on growing throughout the book even though his story arc was marred by the second big plot hole. The second were the fight sequences, the ones that didn't involve Clary, which kept my attention whenever they occurred and had me looking forward to more than a lot of the character interactions.
Before I finished, maybe even before I started, 'City of Class' I had decided this was my last Mortal Instruments book. I gave the series three books and the completion of the first 'trilogy' story arc, keeping my opinions open. However the problems first seen in the 'City of Bones' continued and only got more obvious as the series continued and it has become too much for me to continue.