Dominating <> overpowering. Greg Maddux never overpowered anyone, but he dominated the game for more than a decade by hitting his location with astounding frequency, and late movement. When you have the command/movement that Maddux had, and Lee and Halladay have in today's game, you don't walk people. Look at Maddux, Lee, and Halladay's K/BB ratios. They're silly. 5, 6, 7, 8, to 1 for Maddux and Halladay, and an utterly ridiculous 7, 10, 14, and 8 to 1 for Lee over the last 4 years. Furthermore, you can always pitch directly to a hitter's weakness. If a dude can't hit low and in but kills middle in, guys like Maddux, Lee and Halladay will hit that low and in spot every time they want to. Average pitchers will hit that spot two-thirds, maybe half of the time they aim for it. And when those average pitchers miss that spot, it's at best a ball, at worst a HR. On the rare occasion that Maddux/Lee/Halladay miss, it's almost always a "safe" miss. Maddux/Lee/Halladay will go weeks without missing their spots and subsequently leaving the ball in a dangerous place. When they do have a game where they miss in the strike zone, they get slapped around just like anyone else.
Also, I mostly agree with coolnerd. Neither Lee nor Halladay will have Maddux's career. But for the last 3-4 years, Lee has been as good as Maddux's "good" years, but not close to Maddux's "great" years. Maddux's "great" years of 1992-1998 were as dominant of a 6 year stretch as you've ever seen in baseball. But I think Lee over the last 3-4 years is an apt comparison to the bulk of Maddux's career. Halladay over the last 6 years has been closer to Maddux's peak, though still a notch below.