2. Clichés. There is one aspect of your world that might be considered cliché: the fact that it has a ruined, ancient, highly advanced civilization far in the past, whose demise is shrouded in mystery. Not saying that it can't be used anymore, but just be aware that it's been done a lot, so you need to be sure to add enough uniqueness to it that it feels fresh.
I think you've done a decent job of this so far, actually. Just be aware that you're treading on shaky ground.
4. Creating believable characters, then having them interact in natural ways.
5. This piece of advice comes from Orson Scott Card (it's in one of his writing books, don't remember if it's
Characters and Viewpoint or
How to Write Science Fiction and Fantasy), and it's helped me tremendously:
When doing anything writing-related (plotting, characterization, worldbuilding), keep in mind the two major questions all readers subconsciously ask of all pieces of fiction:
Oh yeah?Would a real person do that? Can a character really take that much of a beating and still keep fighting? Is your characters' use of magic internally consistent with the rules you've set up? Does the world make sense? Do people's motives make sense? Etc. etc.
So what?Let's say your story passes the "Oh yeah?" test. So what? Why should I care about what Aermyst thinks or feels or does? Why does that bit of worldbuilding you just explained matter to the story, or to me? What does a side character's arc have to do with anything, and why should I care? Etc.
This isn't to say that readers are apathetic; they
want to care. They just need you to give them something worth caring about.
So, to summarize: make it real, and make it important to your readers.
Another, related bit of advice (from the same source) is that your work of fiction represents a contract with the readers. That contract says that your characters should always act in character and that the things you've made out to be important amount to something (i.e., if you make a big deal about a character having a knife, we expect someone to get stabbed with it.
This comic rips on Indy 4 for not following this rule, to great effect).
6. So, yeah, I'm gonna ignore your preferred format. Hope that's cool.
Aermyst: Immature, fun-loving, passionate, playful, incompetent, stupid. I've already written at length about how I feel about Aermyst's actions. The thing is, Aermyst's blundering ruins the first part of the book. You gave us enough information to know that a new heart crystal wasn't going to work, and also that there's no chance in hell a soulless Aermyst could beat Zael in a fair fight. You then spend 7 chapters showing Aermyst trying those things - and that's boring! We're anxious to get working on a real, plausible solution (and note that the first attempt should probably fail, even though it plausibly could have worked).
Zael and the Bad Guys: You know, I'm not buying the whole "we're only trying to save the world" schtick. I have seen nothing in your world and the actions of these people that might suggest that's what they're doing. And because I don't believe it, I doubt they believe it either. Zael therefore falls a little flat; he comes off as extremely gullible (you actually believed them when they told you you were saving the world? 'Cause, you know, we're not seeing it).
Mourne, as Head Bad Guy, can be excused for not believing his own rhetoric, but we've now seen that Zael, the underling, supposedly does.
Tristan: Awkward, annoying, unnecessarily mysterious, bright, confident, competent. We don't ever see Tristan's motives for anything he does. He claims to want to help Aermyst, but tells him nothing useful. He drops into Aermyst's life, saves him from himself once, then takes off without even so much as a hint as to where or why. He can afford to be less maddeningly mysterious while still keeping plenty of secrets.
Illis: flat, a minor character, so far mostly irrelevant.
Marlin: sympathetic, likable, determined, intelligent. Not entirely clear at this point in the story why he matters, but he's an interesting character all the same. Not sure it's plausible for him to actually succeed under the auspices of the Wicked Witch of the Sacramency, but he could potentially fail and still be allowed to continue his schooling, with proper intervention from appropriately compassionate and sensible administrators.
11. Marlin is the most interesting character. Tristan is doing the most interesting things.
General comments on the story, and this submission: You seem disheartened. It's true that Crystalheart needs a lot of work to get it into shape. This probably amounts to nearly a complete retreading of the plot and revamping of the characters; the setting can stay mostly the same. So, how much do you care about this story? Do you think it's worth the work to make it as good as it can be? Or would you rather toss it out and start over?
The thing is, we've seen each chapter get progressively better. You've taken feedback to heart and are improving. You just need to stay on that track and keep moving forward.
Of course, there's nothing wrong with simply putting it behind you and starting fresh, if that's what you want to do. I mean, Brandon Sanderson wrote what, like 11 books before he got published? And they won't go to waste: he learned from them, and has been recycling ideas from them into workable novels. If that's what you want to do, go for it. Just don't get discouraged, because I do think you have the seed of a good story here. Only you can decide what you want to do with it.