The conclusion to the trilogy, The Darkest Road was a mixed bag. A lot of the plot felt a bit drawn out and plodding, but nevertheless quite satisfying, especially in the last couple of chapters.
The story picks up where the last left off, with the war between the light and the dark coming to a head. The four ride different roads that converge at battle, and their journeys, both personal and tactical, were well planned and articulated. The drawback of such a convoluted plot, though, is the sheer number of supporting characters that keep coming in and out of focus around the four travellers, and the build-up of interest we get into these characters that isn't justified by the lack of closure in the ending. What happened to Sharra, Coll, Loren, and so many more people after the war is just hinted at. And also,

Spoiler

the return of two of the four to their old world and the impact of their time in Fionavar.

I would have liked to know more.
That, ultimately, is the price paid for trying to compress an LOTR's worth of plot and story into a limited number of pages. It works, but it could have been better.
Nevertheless, the book really delivers, especially on the aftermath of the war. Almost all threads are neatly tied up, and there is a genuine sense of loss that the adventure is over.
The whole trilogy is a really good exercise in fantasy, and definitely a series worth investing the time in, even if it does raise some doubts along the way.