Today Star Wars: The Old Republic launches. My character is level 20 after a week of low-intensity playing, in which I had a lot of fun. If you haven't bought the game yet, I can heartily recommend SWTOR for its excellent story-telling, polish, and leveling game.
I do not, however, have much faith in the endgame. The strength of SWTOR is clearly the way the stories are told, the cut-scenes, the voice-acting, the decisions you can make in conversations. All of this is content which is great once, but quickly diminishes in fun when being repeated. And I haven't seen anything to suggest that the endgame in SWTOR isn't like the endgame in every other MMORPG, which means playing through the same content over and over. And seeing how I already met characters in their level 40's before the game even released, I'm afraid reaching the level cap will be all too early.
As far as I can see you can play through SWTOR at least twice and get a completely different story, once on each side. If you don't mind partial repetition of quests and zones, you can play through the game 4 times, covering all 4 starting zones and all 4 base classes. That is good entertainment for some months, depending on your speed. But if you are looking for a game that keeps you entertained for many years, I am not so sure SWTOR can provide this.