The Mortal Instruments series originally ended as a trilogy, and it was a pretty good ending that felt like an ending… but then the author decided to extend it into a six-part series, the fourth and fifth of which (City of Fallen Angels, City of Lost Souls) are something of a slog. They just feel completely extraneous, as if they don’t really have anything new to say; existing solely to drag the story out and ruin the conclusion of the third book. The sixth however (City of Heavenly Fire) is actually fairly engaging and almost justifies the existence of the two preceding books. The ending isn’t really an ending though and it handles the Simon issue rather horribly.
Hardship and Damnation are the final two books in Jean Johnson‘s Theirs Not To Reason Why series. The first of them is only so-so and seems a little forced and overly limited, but the second works quite well and wraps the series up nicely. I can’t say I’m not interested in a sequel that covers the future timeline that this series spends so much effort preparing for.