We're gonna have to agree to disagree then. I've also been with the game since before launch and while I've taken a couple of breaks of 2~3 months, and I feel once you've gotten to the daily missions, and ran the story-expansive raids once, you've seen pretty much everything for that character. Makeb is pretty nice, but it doesn't open everything up. For the record, I've got one 55, one 50, one 42, two 39s, and one 22. I've also run a lot of dailies and FPs for the 55 and 50 because the 50 was my "main" back when the game first came out. I will admit that I have limited experience with PvP because it was such a mess at launch and I just didn't want to fiddle with it after that.
Well as I said, it depends on what you like to do and what you want to accomplish. It sounds like you just wanted to see all the content once and then you were done. That's fine but that seems like an attitude brought from single player games and not MMOs.
People talk about "grinding gear" at end game in most MMOs and this is true but it's really just another form of progressions and MMOs are all about progression. So at end game it becomes a new quest to no longer gain levels but to improve your character with better gear. To that end SWTOR offers many paths to get there, especially now. I admit that I PVP a lot, I love the PVP in this game, so this always gives me something unique to do because PVP matches are always unpredictable. For PVE you have a lot of ways to improve your gear or stats:
Daily quests - there so many now that you don't have to repeat the same ones often (Ilum, Belsavis, Black Hole, Section X, Makeb, GSI ones on Alderaan, Tattooine and Hoth)
Flashpoints
Operations (Story mode, hard mode, nightmare mode) x 8 and 16 man versions
While doing the same FPs and Ops multiple times might be boring for some I feel like the fights are generally fun enough to bear repeating. Especially the new operations.
On top of that I've spent many days hunting datacrons and trying to figure them out on my own. Sure you can find videos and guides but that ruins the fun IMO.
After that you have:
World bosses
Space missions
World events (these are obviously rare but they have given me something new to do every few months when they occur)
Then you have things that don't improve your stats at all that I spend a lot of time doing:
Collecting rare pets
Collecting orange/adaptive gear (including some rare/hard to get stuff)
Collecting rare mounts
Achievement hunting
Rep grind
Gearing companions
Crafting
Buying/selling
and yes leveling alts
So on any given night I have dozens of things that I can do and while yes you need to repeat content there is enough of it now that I don't repeat it often (except PVP). Sometimes I'm doing stuff to improve my characters gear/stats but sometimes I'm just playing dressup and creating different looks. Sometimes I just hang out and goof around with my guild or help noobs or chat with friends. It's all part of playing in a multiplayer game.