Closing the second trilogy of books, The Chapter's Due presents a quite weak and simple story of chaos space marines and daemons attacking the homeworlds of the Ultramarines.
The interesting points are a lot of battles and an abundance of known heroes: Uriel, Tiberius, Sicarius, even Maernus Calgar.
But even with all that, the book has a dumb plot, unexciting events, unrealistic battles * and in general feels more like a book just written to close the trilogy instead of because of having a nice story to tell.
* Sometimes a lot of space marines die against normal enemies, while other times a bunch of them kill all that gets in their path.