I won't go out on a limb and say it will be the World of Warcraft killer, but I definitely think it easily has the best chance to become a solid and long-lived competitor. It's got the Star Wars name brand, the graphics look stellar compared to WoW's now dated look, and the gameplay looks 5Fast5Furious (don't hit me Vin Diesel) . It's probably best for the MMORPG industry that some new, viable blood is going to pumped into the mix.
I'm not saying there is going to be an arms race of gameplay awesomeness between SWTOR and WoW, but some friendly competition can't hurt anybody - hell, the players will certainly benefit.
Here is a 20+ minutes of nice gameplay footage from PAX: East to get you salivating (also a bonus cinematic below that!):