I spent a few delightful minutes at the Nintendo booth playing Metroid Prime 3: Corruption, and displaying my poor sense of direction to a crowd of onlookers. I got just enough playtime to test out the controls (I didn't need to beat the game or anything!) I can safely say that after about five seconds of fantastically awkward movement, I felt not only comfortable playing the game, but, like with Zelda: Phantom Hourglass, I was enjoying just messing around.
The controls are exactly the same in normal or expert mode, with the exception of Wiimote sensitivity. Expert mode is way more sensitive, and requires much subtler movements. It also enables quicker motion. Looking around and turning with the Wiimote was awkward at first, but it immediately clicked and I was ready to run and jump around. Shooting, of course, is mapped to A, and jumping to B, so there was no problem there. Z on the Nunchuk locks on, and C activates the morph ball. Down on the D-pad shoots missiles. All of these worked well and intuitively. The only exception is scanning: I never quite got it, but it basically involved holding Z, moving the Wiimote to point at an area in the corner of the screen, then holding Z again. It's the only part that I can honestly say takes getting used to.
The best part of the controls is easily the grapple beam, which involves targeting a grapple point and making a lasso motion with the Nunchuk, then pulling back. Once I started doing that unconsciously, I felt pretty cool (I wasn't.) It seems that Nintendo has finally found a "hardcore" equivalent to Wii Sports: if not in popularity, at least in deriving actual enjoyment from the basic control scheme.
Oh, and, in case you were wondering, the game looks hot, especially on those big fancy screens Nintendo was using at their demo stations. We should all get some of those.