playing from 1-50 then another class up to 40 there are things that are easy to spot which is what made it fail.

-The ability to choose/create your story. Load of BS the "choices" are a poor gimmick which only manipulate the idea that your choices make a difference but really don't.

It honestly goes, well if you kill this person and the other person doesn't kill this person, that just means this person is only used in this story arc so whether you kill them or not has no real influence on the overall game plot. So your option to choose is nothing more then wasted resources that could have been spent on other parts of the gameplay.

-PVE and PVP balance. In their attempts to balance PVP they ended up nerfing PVE builds which pissed off a lot of people since the concept of a sneak attack imperial agent operative was pretty much deemed worthless ONLY because people were moaning for a nerf through PVP not PVE. Rather then just adjust abilities for PVP they just adjusted it to be the same for both PVE and PVP which pretty much made said build worthless.

-3 Skill trees so you can "customize" your characters but not really. So you have 3 skill trees but in all honestly maybe 1-2 builds are good and if you find a build that's to good it'll be nerfed for being to good, so because you found a build you like you are punished for it and have to make a new build and playstyle because of it. Something like this comes down to poor playtesting, this is what happens when you give each class to many abilities to work with, it's harder to find what works and what may be overpowered. Unlike in 14 where we currently have a simplified ability list but because of this simplication it's easier to balance the game overall and prevents the complicity of accidently overpowering or nerfing classes.

-Adjusting classes on a one by one basis. You should never nerf a class without seeing how it looks in the bigger picture, this goes back to the operative PVE/P nerf. So let's say in terms of ability you have 1>2>3>4 all the classes are imbalanced, so you go well that's not good we need to change it up so you change 1 to weaken it and add something to 3 but then you do this 3>2>4>1, now you've weakened 1 to much and have just made it to worse class. In a game where you aren't free to change your class on said character making a class you play feel worthless is a good way to lose subscribers. When it comes to balance more time and care needs to be taken into it so that it's 1=2=3=4 and not 1=2>3<4 kinda bs lol.

-Hitting 50 made crafting worthless. The gear from crafting became worthless once you were able to get the exclusive gear through the point system involved in pvp and the instances you could do, because of this only biochem was considered worthwhile because of it's reusable cures as well as exclusive medicines that only biochems could use which granted them with more attribute boost then the refular medpacks.

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Overall it just comes down to poor design focuses, if you focus on making decent gameplay first and an intriguing story it'll draw people. But when people play an MMO they want something that's different from WOW but at the same time they want something familiar enough so that they can adjust to the gameplay easily.

SWTOR only survived because of it's brand name, had this game been released by any other name it may have started with 1/20 the audience as only have 1/200 left by now lol.

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An mmo should never be based on "unique gimmicks" which add nothing to the overall game, if you want an mmo with choices that make sure those choices actually effect gameplay, FFXI had more choices compared to swtor when it came to campaign the choices you made for your nations strategy was put together based on other peoples choices to influence how they would act the following week. yet there's nothing in swtor which would suggest that choices made actually mean anything more then simply being light or dark lol.

They relied to much on the brand name, just like the original FF14 did but that failed faster because of how obvious it's shortcomings were. The reason why SWTOR lasted as long as it did is because of it's promises and it's attempt to connect with the community going as far as to have a guild summit months after released.

The thing about mmos is you shouldn't create something and say this is the reward. You should create a wide variety of things and have the player decide what their reward is. Such as with the suggestion that the beastiary will be added, it's something those interested in beastiary can do and enjoy while others might be more interested in fighting in hamlets or seeking out the roaming primals. You need a live open world to keep things interesting but also have to keep in mind that you want people to play a challenging game but you don't want the "challenge" to include things like a heavy reliance on claiming over other groups which is just no fun and a complete time sink found in older mmos.
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But ya mmo should never rely on a gimmick as it's main draw "completely story driven" gameplay aka "one player experience" lol SWTOR was pretty much a single player game that you played with others around you and maybe if you were bored would team up with them to do other events.