Most fiction (and any storytelling for that matter) exists on the idea of suspension of disbelief. Ragnarok unfortunately fails this test. I mean unfortunately, because I enjoyed much of the book.
The book is best when it deals at a tactical level. When it tracks events, such as the details of a battle, it flows well.
But it fails in two ways. First, the villains are cartoons or worse, sometimes sketches of cartoons. They are either filled out in ridiculous ways or they are not filled out at all. The "traitor" in the book is mentioned only in a couple of paragraphs, but the traitor acts in ways that are ultimately stupid even for her own motivations (ie, ultimately she puts herself in mortal danger -- which is not her intent). David Weber often draws his villains broadly, but not to the point where they are only two dimensional. Patrick Vanner's villains are not believable.
Second, in Science Fiction, the author can create the universe any way they want, but it has to be consistent and logical. Mr. Vanner creates the climax of the book and the basis of the next book, by creating an artificial crisis which is neither scientifically or militarily logical. He suddenly introduces nuclear weapons with no explanation about why no one has used them previously in the book. If they were available all of the military tactics in the book would be different. Vanner can create a universe in which they are available or they aren't (maybe a nuclear suppressor or shielding), but not both without explanation. Given that nuclear weapons are available, the human side's actions are not logical. You would have a completely different system defense strategy. Actually everything in the book would be different. Again Weber in his Honor Harrington books deals with this logically (various types of shielding), Vanner, not so much.
It is fun at some levels, but Vanner's editor should have cleaned this up before publication. They did him a disservice.