First off, let me say that this post will be filled with spoilers, for obvious reasons:
Having played through Chapter 15 so far and a few days away from the Final Release, I feel I can provide my opinion to the overall story of the Knights of the Fallen Empire expansion.
The beginning starts out semi-promising, with your Character conferencing with Darth Marr as you search together for the Emperor following the events on Ziost. The capture and interrogation with Valkorion was okay, but I feel that your decision on whether or not to join him should have had a larger impact on the story - maybe resulting in you becoming the just like Valkorion, your sworn enemy.
This was a cool story tool that we got to see for a second in the JK story on the Emperor's battle station. Seeing how your companions react to your ultimate betrayal would have given those characters more depth. Even after the first few chapters, the story already begins to take a dull turn. "Recruiting allies" in the Lady of Shadows and the Scions was EXTREMELY boring. The story could have been much more streamlined. I don't think it was necessary to lose all your companions for the first nine chapters.
In my opinion, they should have been there with Lana depending on if you had a good standing with them with Influence - this would have been an interesting and unexpected mechanic they could have added. Senya and Koth, despite their backstories and conflicts, are extremely flat characters that fall on their stupid faces right as we enter Asylum. It's hard to feel a connection with them after you're just pushed into each other by BW.
Each chapter in the storyline should have built not only the overarching story, but also your relationship to all of your followers. Instead, all we got were some corridor filled mobs immune to stealth and knockbacks without any reason for strategy. The gameplay actually drags down the main storyline numerous times. Right when you feel there's a hint of action, more Skytroopers spawn in.
The main plot is an interesting idea, with a new faction we didn't even know existed. However, one of KOTFE's biggest mistakes was the Alliance. I know, I know. "Isn't that the whole point of the later chapters?" However, all the Alliance does is make you feel important until you realize that there are a bunch of Outlanders running around with the exact same story as you, some of them being the enemy.
In its effort to make your character a key player by surrounding them with powerful allies, I feel like some lowly Jedi who just answers questions but doesn't make any important decisions. Conversations have very little impact on the story and do nothing to enhance your own character's well.....character.
I don't feel like my character has learned much of anything throughout their experiences. In the original class storylines, every class story was filled with intrigue, deception, character growth, and satisfying combat. Now, we have to wait for more chapters to get a chance at any ONE of these - except for combat of course .
Bioware needs to go back to their original formula with the specific class stories, where it matters what class you are, instead of only knowing when you are being referred to when somebody says "Master Jedi", "my Lord", "Captain", or "Major".
Let me know how YOU want the story to change from KOTFE into KOTET, the upcoming expansion.
P.S. Thanks for listening to me rage a little at what could have been
Edit: Thanks for the feedback guys. Fixed the paragraphs. Looking back, I wouldn't have even wanted to read that