Having played through early access, I wanted to give my 2 cents on the new expansion/content as others have done. It seems the devs want feedback, but I also hope this will be helpful if some players are still on the fence about subscribing for the new story content.
I am not going to pretend I have played through every option or dialogue branch (only the Jedi Knight story) in the new content so I cannot speak for the imperial side or other classes.
First of all dev team, the new story (in my opinion) is really good. The voice acting is top notch. This is the first time since launch that playing through the story hasn't felt like a long grind for me (trash mob overkill is another issue), it made me laugh out loud at times, made me feel emotionally connected with the characters, and quite frankly I could not stop playing just to see what would happen next. Amazing devs, just damn amazing.
Is the new content worth a month's sub? Yes. No doubt. Do it. You won't regret it.
Should you subscribe after the initial first 9 chapters? No.
Having finished the chapters given in early access and seeing how short they are, even with trash mobs thrown in everywhere just to give the illusion of the story lasting longer; only releasing a chapter a month is simply not worth the money. I recommend waiting until late next year when at least another 9 chapters will be out to experience it.
Unless you must have unlimited access to pvp or pve, stay free to play. You can see the cinematics on youtube for the story as well, so you won't be missing out if you just have to know what happens, but again save your cash.