I started reading this book and as a bit disappointed that ther LotD weren't prominant. But by the end of the book I actually liked the way they were portrayed and weaved into the story.
The fact that they appeared in response to a prayer to the Emporer was good, that they were a manifestation of His will. The way they haunted the protagonist after he survived a masacre and helped him redeem himself (even if the chapter standard is still missing and he's led a full company to their doom). The revelation that the Space Marine wasn't the only one seeing visions of the LotD was great.
If the book had been totally about the LotD fighting battles it wouldn't have been good. Instead we get a story about how they present themselves and help those in dire need, a story that explains a lot about them, yet retains some of their mystery. I thought it was great.