For those who didn't know, and aren't planning to play the game...
The upcoming expansion will be the prequel to the last expansion (Knights of the Fallen Empire).
KotFE was the expansion that pretty much did away with any new raid content, and made group content nearly obsolete (just a few new heroics). ALL of the new story content is single player story mode only now. The KotFE story is more suited to force users (dark or light), although the story is basically the same for all classes. I ran through it with a commando and gunslinger, and it just didn't feel the same as it did with my knight. I'll probably run my Sage through it as well...
The last expansion also completely changed the companion system. Everything is the same for the planetary content (leveling and flashpoints and such), but once you start the Knights of the Fallen Empire (level 60), you lose all of your companions, and begin a series of missions to recruit new ones (almost all of the old story mode companions and quite a few more) for your mission to defeat Valkorian and the eternal empire. Once you have recruited them, the idea of having access to a wide variety of companions seems kind of fun, except for the fact that they all have *exactly* the same abilities (companions can now be any role - heals, tank or DPS), and all that changes is their physical form and the one liner statements they tend to spew while you are running around with them. Also, companions 'power' is now exclusively determined by their affection for you (they no longer get stats from gear or weapons). Affection is still raised by giving them gifts, which means if you want to have multiple *powerful* companions, you'll need to farm a *lot* of gifts, in order to keep them all happy.
I ran through KoTFE a few times on alts, but the companion affection farming was just too much. I have 22 alts at level 65, but only a few are in end game gear and have high affection with companions. I mostly stopped playing except to log in and run through new chapters as they were released.