So I always like to write my reviews in three stages: Grammar, Characterization, and finally, Overall Story. That way, each section is given their own time to be focused on with no overlap, not to mention helps in showing you which areas you excel at and which ones you might need a little help in. Other than that, let's get started!
Grammar: It's stellar, no need for change at all. I also see that you have it published on Amazon, so you definitely had gotten an editor for it, and it shows. That's great because it means that its readability shouldn't be much of a problem, and any clunkiness won't be based on any run-on sentences, comma splices, or improper spelling. A+ work!
Characterization: It is an excerpt from a different book, so I'm guessing that these are either characters we're to be introduced to in that story, or ones from a previous book that I don't know about because I haven't read that story. Whichever the case, I'm not given much, besides their names and mannerisms, to get a solid feel, with Czarclana in particular. The Witch is dangerous and should be feared, but that's it. She comes off as your standard Evil Queen, but there isn't much that makes her uniquely Czarclana. What's her motivations? World domination? Why? Does she want to completely destroy the world (do villains not know that doing so will destroy them too or is that part of the madness okay I'm done), or just change society into her image? Are we talking about someone who wants to be a god, or who believes, in some twisted way, that she's saving humanity? We see a snippet of this when she says that she'll have control of the Seven Artefacts, but we're not given any explanation as to why she wants them. A perfect example of showing this would be Macbeth, who wasn't a villain initially, but due to his unchecked ambition, slowly became a monster. If you could include her motivations that's under the surface level, or use it as an example for the other characters also, then you're on the right track.
Overall Story: Your descriptions are touch-and-go. When they're good, they're really great. I don't normally like battle scenes (not to mention hate writing them, everything always ends with "X punched Y because he was a meanie. Y poked X in the face") because things can get pretty cluttered pretty fast, but yours is stellar. My favorite part is when the Bolt Thrower completely decimated most of the Predakren hoard just on his own. That's some power right there! However, there are also moments where there's a serious lack of descriptions, such as explaining to us what the characters may look like, the sheer volume and weight of things, etc. I accidentally explained much of this in the "Characterization" portion above, so I won't go into too much detail on that, but I will also add that your exposition is a bit overdone. Most, if not all, of what the characters say is information that could be shown to us instead. For example, if you mentioned the Legends briefly in the beginning, but then later showed them to us in the battle, and we get to see the full scale of who they are and their abilities, it builds up the reader's suspense and intrigue when they read about them later on. It's much better than explaining everything at once initially, as it loses that suspense (unless you do a twist, in which case, don't follow Season 8 of GoT. That one's a doozer).