I just finished FF XV main story (which with sobe sidequests and wandering around world took me about 30h) and first time I am so disappointed by the fact how story was told and how such huge potential it had. 

Don't get me wrong, it wasn't anything new and spectacular in main story, but first time in a long time I really wanted to understand it (FF XIII story was so fcking horrible). But the way it was told was bad, ugly and not in FF strandard. The only ones I really cared of were Noctis and his friends. How could I care about Regis, Luna, even Emperor when they almost did not apear on screen? Seriously? 
How about Caligo (bet you guys don't even know who am I talking about xD), Ravus (they did not explain why he was with Niflheim) and other characters that game did not let me to care about?
Most complete stories where Cid's, Aranea's, Cindy's and that boy's whose father or grandfather was killed in Lestallum (characters who are not so relevant for main story).

And why Noct was 10 years asleep? Did they even explained it? Why Ardyn let Noct go and do whatever their wanted?

I watched movie before playing game and if I haven't I am sure the story would be so fcked up and full of unaswered questions that I would not understand anything. And how does it comes that you have to watch movie to understand game? Stories from movie could easly be added to game.

I can write on and on but the point is that this story really had such huge potential it could be told so much better with so much details and better care for telling stories of other characters and it makes me so sad that SE forgot what has been the strongest part of every FF game.

BTW. I think story in Kingsglaive was so much better told than in FF XV. I guess making things faster gives better effects ;)

I think the biggest mishap is the way they handled Luna. She needed much more exposure for us to care about her. It made her death and her whole purpose irrelevant.
The rest of the mistakes have become customary in Final Fantasy games. FFXIII also had the potential to have an incredible story but the storyline was too messy and convulted.

I agree, there's just so much wasted potential there. It could have been truly great.

Ardyn wanted a worthy opponent(the True King) and also wanted to destroy the crystal. Without the Crystals power, Noctis will not be able to do anything to Ardyn. So I guess with Noctis absorbing the Crystal, Ardyn would be able to satisfy his needs, which is destroying the True King, fighting a worthy opponent and destroying the Crystal.

Also it is within the Crystal that Noctis learned about his mission(thru Bahamut), who Ardyn is and such. 

So Ardyn actually helps(and annoys) Noctis on his journey so he could get to the crystal because that is what he wants.

I dont mind the way they handled Caligo and Loqi because they are secondary - or even tertiary - villains. The fact that you can encounter them more than once is good enough for these kind of characters. But the way they used Luna, Ravus and the emperor is just dumb, they were important characters story-wise and they were not built properly. Hell, even Verstael could've used a lot more development. So, while I personally did enjoy the game and did enjoy Ardyn as the villain, the overall lore and story does feel weak and not developed.

ok, but why he was asleep/away for 10 years?

How did he die in this fcking chapter 13? He was turned into monster? All I saw was his clothes (I guess) in this round room.

I've become convinced that this is something the Japanese like.  RPGs with stories that devolve and twist back upon themselves in order to create an illusion of complexity are way too common for it to be a coincidence.  

Yeah, I guess you are supposed to assume he turned into a daemon because he "dissapeard" and thats it. So wasted character after they link him to Prompto. 

Alternatively, maybe he'll come back as the villain in Prompto's DLC? Maybe? I hope that happens cause it'd be a waste if not. 

That's the time it took for Noctis to fully absorb the Crystal. Why 10 years? I have no idea.