Ever since information started coming out about the Fallen Empire expansion, I have seen comments that 'the game they love is changing too much.' This feeling is partly BioWare's fault due to the way they have been releasing information. I think a lot of it is misunderstandings though. The game really isn't changing that radically.
Questing. Doing quests in SWTOR is going to be the same as it was before. Still voiced and with cinematics. Leveling will be almost all about your class story, like it is now with 12x xp. It is unclear what will happen with the one-off side quests.
Combat. Still the same, with some minor stat changes. New ability for each class.
Classes. No major changes, just 5 more levels.
PvP. No changes here (sadly).
Companions. There are mechanical changes with companions, but overall they are staying the same. You'll still get them while you'll level up and they'll still have their quests. There will still be romance, if that's what your into. You'll now just be able to use them in any role, and also be able to get more of them. You don't have to lose any companion from your class either as BioWare made a way for you to obtain them again.
Flashpoints. They aren't going anywhere. In fact, they will all now have solo modes, and be available to the level cap. So if you missed them while leveling, they are still there for you to do.
Strongholds. Still there.
Crafting. All indications are that it remains basically the same, but more streamlined. You'll still be doing crew skills too.
Operations. They will now all be available at the level cap. So if you missed any due to playing later in the games life, they'll be useful to do again.
Fallen Empire. We'll be getting a new story, with monthly updates. There will be some 'break' with the pre-60 game, but you'll still be able to go everywhere you could before.
Oulander. Just a name, there will still be class specific dialog/flavor. Although no class specific quests :(
BioWare has been building towards this since Shadow of Revan. So I would not expect something radically different than that and Ziost gameplay wise. There are a lot of changes, but the way you play the game will still be pretty much the same. You may have to think on choices more :)
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