Preface: In the interest of full disclosure, I would like to say I personally know the author, but if anything, it would cause me to be more critical of his work.
Preface II: Author originally had some mechanical and consistency errors, but edited them out. This review has changed to reflect the current state of the book (after 10/20/16).
I'd also like to start out with highly recommending this book, especially if you're into video games like World of Warcraft or role-playing games in general, role-playing games like Dungeons and Dragons, or even just the fantasy/dungeon diving genre. It is a fresh twist on a familiar concept which is really needed in fantasy as a whole.
Overall, I felt the premise was very promising. It was different in that it (often) focuses on dungeon diving from the viewpoint of the dungeon rather than the diver. This provides an interesting outlook while still providing the otherworldly fights we fantasy readers crave. For someone who doesn't want spoilers, the best description/review I can give of the book is that it is a story about a dungeon, from conception to a place filled with death and danger. It is also a story of character evolution from both the dungeon and some of the divers which enter its maw.
Pros: The author found an interesting concept and ran with it. He didn't allow himself to be too bogged down in the gimmick of making the dungeon sentient. Using Dale as a secondary main character works well to get us out of the dungeon from time to time. The premise is mostly unique and pays off beautifully. The magic system is actually my favorite part of the book and is extremely intricate while still easy for the reader to understand. The concept of runic symbols/inscriptions vs enchantments vs incantations keeps things balanced in that magic can be done by anyone but can be extremely dangerous at worst and extremely taxing at best and in that it provides both flavor and diversity to the magic. The creatures in the dungeon and the way they are created is incredibly insightful. The humor lines up directly with the author's humor and made me chuckle (if not flat out laugh) at work a handful of times. The world is incredibly well described and detailed, although it still feels as though we learn new things throughout the book. The characters are typically likable when they are supposed to be and unlikeable in the same token.
Cons: The cons in this book are more about personal style than actual poor writing and are better described in the mixed bag section below. Honestly, the part about this book that made me the least not happy was the last page. Nothing about the content on said page, but that it was the last page. I wasn't ready to transition into a second book quite yet and felt some loose ends were left a bit too loose, but then looking at the length of the book, I can understand why the writer wrapped it up. In fact, I feel like the ending itself was a great way to spur on the sequel, even if there are some questions burning in my mind.
Mixed Bag: There is a ton of exposition, or world building, in this novel. I quite enjoy it, but many do not enjoy this level of exposition. Also, there is very little physical movement in the book. The only places the story takes place is the Phantom Mountains (specifically the mountain Cal is in), inside of Cal, and a short bit in the capital city. Cal, being a dungeon and all, doesn't move much at all. Again, I feel the author does a good job spicing up the environment and flat out changing it to keep things from getting stale. Other than that, some people may point to rapid character development as a flaw, but that is clearly explained as the side effects of the refinement of essence and the ranking up of characters, and I feel it is well thought out and well explained.
When it comes down to it, I give the book a 10/10 focusing on the concept, the actual narrative told, the wonderful world that is built, the magic system, and the humor while the only knocks against this book are those listed in the Mixed Bag section, and I personally enjoyed those parts of the book. Out of a 5 star system, a 10/10 obviously equates to a 5/5
I highly recommend this book and look forward to learning more about this world and the characters in it in Book 2.