Looking closely the issue is not gameplay so much, but the difference between the single player and multiplayer experience.
From a historical perspective, I believe TOR is laying a very huge foundational stone here. They are making a game that is 8 games in one following each class, with no class missions that overlap, world missions, epic storyline, and complete voice over. But this my friends, is only the single player part of the game. Regardless of how they do it, I'm sure all of us (GL, SBR, et al)will want to play through it. I know I want to tell my kids I played this game I believe it will leave that kind of a landmark much the same as Final Fantasy did for RPGs.
As for the multiplayer experience - I believe that is the real issue for most of us - we don't know how all that's going down just yet. We all enjoyed NWN and then GuildWars, I can only hope that this will blow those out of the water which I'm sure they will. (If they throw in space to be sure!)
The bottom line is we will play it, but the question is: How long will it hold our attention?