It's Star Wars, a franchise that practically everyone knows & loves (or loves to hate) & BioWare, the company whose star shines brightest on the cRPG firmament. A deadly combination.
The real issue is whether or not
The Old Republic will have long-term staying power, and also how quickly its developers are able to release new content.
BioWare is a top cRPG developer, but they're new to MMORPGs, and some of the decisions they've been making (100% voice acting for all NPCs being one example) lead me to believe TOR might be a "casual, done with it in a month" sort of game. I'm not saying it won't be fun, but I
am saying that MMORPGs without enough content to keep people interested for many months are ultimately destined to fail.
World of Warcraft accomplished what was formerly considered impossible: It caters to both casual and hardcoe players at the same time, and also stays addictive month after month after month after month.
An MMORPG based around storytelling,
a la single-player cRPGs... well, great stories can only go on for just so long, and it's rare that any computer game with a decent story can't be completed in under a month. All of the Black Isle games, all of BioWare's games... hell, every cRPG ever released can be completed if you put in two hours per night every night for a month, or two at the outside.