I was in the SWTOR beta and it was rather fun. I played exclusively Empire and played up to Belsavis twice, the first time right before a beta wipe and the second time I burnt out really hard there (mainly due to lack of friends to play with).
After the game launched, it managed to pull in a lot of my old friends/guildmates from SWG and other games, but not many people stuck it out once the content dried up (at the time there was your character story missions, then once those ended it was basically either broken crap PvP or endless raids). I myself didn't because I had terrible internet at the time and it made it impossible to do anything (I remember racking up so many deaths due to lag on the falling Rakata platforms).
It was a fun game. Ultimately it was just a Star Wars-Themed WoW clone and WoW never could hold my attention for long. I think it also suffered from the fact that too many people were hoping for a relaunch of "SWG, only better", which the game was not at all. I also think people were annoyed at having to play with systems that WoW had and had perfected. And I think that the fact that their content was so big (in terms of scale and time spent to make it with all the voice acting and whatnot) hurt the game because it did take a while for there to be new content after the original story was done. Beyond that, it was hurt by subpar endgame content at launch and the subsequent scramble to fix it, as well as the fact that the storylines were basically meant for a singleplayer game (id est, every bounty hunter becomes the best in the galaxy and has the same set of companions), and terribly linear planets and storylines.
Beyond all that, I did greatly enjoy my time playing it with my pals. Working out how to get holocrons and all was fun, as was what little exploring there was to do, and the stories were masterfully crafted and incredibly fun to play and progress in. I've heard there has been a lot of improvement in the game since I quit playing (a few months after it launched), and the fact that it's free to play is also very tempting, but I'm not a fan at all of how steep the restrictions on free accounts are, and I feel like veteran players like me, who not only preordered and played at launch, but also beta tested the game, should get some kind of status or some sort of bone thrown to us to make coming back a bit more worth it.