If I had not read the first book of the Obsidian Trilogy, it would be very difficult to avoid being critical of this second book in the trilogy. To Light A Candle is less a sequel than it is an opening and a collection of cliffhangers for the final book in the trilogy. It contains so many open-ended introductions of new characters, new threats, new powers, and new applications of ancient powers, that I can't see any way for Lackey to tie up all the loose ends within a single book, but I guess that's why she's writing the books and I'm just puttering around filling up pages with reviews.
I am somewhat surprised at the minimal conflict of opinions over this novel demonstrated by the reviews present here at Amazon. From my reading of other book reviews, I have come to believe that there is a large group of people who are immediately opposed to any use of clichéd fantasy elements, almost all of which Lackey has used in this trilogy (Please read my review of The Outstretched Shadow for a description of those elements). However, the cliché present is minimized by her over-arching world and character-building focus, particularly referring to Kellen's internal, personal doubt and the world's extremely well defined systems of magic.
Two things make To Light A Candle stand out as an engaging book. The first bit deals with Lackey providing us with a different perspective of Kellen and the changes he has gone through since being kicked out of his old home. One of the newly introduced characters was a star student and classmate of Kellen's in their former home. This high-magic practitioner, an interesting addition to the motley crew of elves, dragon, assorted wild-mages, and centaurs, was banished from Kellen's old home-land, much in the way Kellen was, and from this newcomer's eyes we gain this new perspective of Kellen and how much he differs from the frequently whining and indecisive whelp that was kicked out of his home-city for practicing a banned system of magic.
The second interesting element of this particular installment of The Obsidian Trilogy, in my opinion, is the demonstration, occurring near the end of the book, of how the two seemingly disparate types of magical systems, "High" and "Wild" magic, can be combined to deal frighteningly powerful blows to the insanely powerful "Endarkened". Also, the continued growth of Kellen's power, or at least his use and understanding of that power, is fascinating, as the power Lackey grants to her "knight-mage" is not a direction taken very often in most formulaic fantasy novels. Its entire nature is internal, more akin to having a second, more knowledgeable and far-seeing mind bolstering Kellen's own, than to any fire and acid slinging mage from other recent fantasy books. This kind of internal magic isn't seen as often in formulaic fantasy as it is in other types of adventure fiction (I can't think of anything else as similar to Kellen's magic as is Peter Parker's "spidey sense").
All in all, To Light A Candle is a fun read, with engaging battles, interesting new characters, new twists on old characters, and new threats seen in every shadow. I do recommend it, but only after you have read and enjoyed The Outstretched Shadow. As I said earlier, To Light A Candle seems to be primarily dedicated to establishing a stage for high drama and great action in the third and final book of the Obsidian Trilogy. All that remains to make this a trilogy I want to keep on my shelves to read again is a stunning final act.