KOTOR was a good game and the best thing to come out of Star Wars since the original trilogy (which may be damning it with faint praise). I probably should find it more interesting than I do, but the fact is I'm just so f'in sick to death of Star Wars that the IP is working against it instead of for it. I also can't even begin to tell you how old it's getting to watch badly animated jedi bounce their lightsabers off enemy troopers and droids as though they were long swords +1. This is part of the problem with the iconic weapon of Star Wars...realistically you should be able to run around one-shotting everything with it. I want a Star Wars with fluid, action-oriented game play, like the Jedi Knight series, more than I want to queue up "Power Attacks" and watch bad canned animations loop.
So, to make a long story short, KOTOR was probably a richer and more traditional RPG, but Mass Effect was a far sexier, more propulsive, and more cinematic game. And since it doesn't suffer from the Star Wars taint, I take it 10 times out of 10.