I think I had two big problems with the game, both caused by my incessant Altoholism.
1) You will always level in the same places. There are no alternate zones, there are no Optional planets. There are bonus series, but in general you will do the same planets in the same order. Always.
2) The legacy system stymied my alts. Because so much of it is gated by huge costs and not just simple unlocks I had to more carefully plan out what alts I wanted bonuses on. Did I want to drop 500k on a character for faster levelling just to experience the story? I would make the money back over it's lifetime sure, but that's a big dent in the wallet of someone who also goes out to purchase Legacy armors along with gearing his own characters for various tasks at 50 (You may not believe it, but I've played since before open beta and still have only ever completed a single raid, HM KP).
I realize I'm not everyone of course! I'm not good at collecting large sums of money or knocking out content, but I love the stories. I took a month break or so to test out GW2 (Imagine my disappointment at the corpse running zergfest dungeons and the sad matter of only getting cosmetic gear at the maximum level. I can't even make past content easier because of level adjustments! Still a fun and pretty casual game though), but now I'm back and must say I've missed TOR. I missed the plight of a quest giver, or the dramatic tempo in the background as my Sith rises in power, or thematic pull at my heartstrings as I must confess the truth to a new widow. It just...has that fun factor. We may get burnt out and wander off.....but I think I'll still come back to TOR as long as pulse beats in the servers.
....too bad my server is sparsely populated! Even then, I shall endure with my guildmates!