Nintendo originally promised a controller that could basically detect motion, tilt, depth, angle, orientation, and position of the controller in a 3D space. (not sure about them specifically saying 3D space, but the others were all promised) Instead, we got a controller that tracks orientation well, tilt ok, and depth poorly only if pointed at the screen, tracks basic motions if not pointed at the screen, and that's it. WiiMotionPlus brings the remote a lot closer to what their original vision was
Compared to what was promised when the Wii remote was announced, what we actually got fell far short and severely hampered the applications of motion in Wii games. There's a reason that most of the time there is motion in a Wii game, it is just waggle or always involves pointing at the screen. The tech isn't capable of doing much more with any kind of precision or consistency.
I distinctly remember SSX Blur, which was a near-launch Wii game that based the game mechanics around doing relatively complex gestures with the Remote for higher-scoring tricks. They were designing a game around what they were promised the Remote could do. When they found the Remote wouldn't be anywhere near as precise as what they thought, they couldn't redo the entire tricksystem/control scheme in time. As a result, the game was nigh-on-unplayable, the game bombed, and we haven't seen a single thing from the franchise since. Also, you haven't seen any more games try and put complex gestures in the center of their game mechanics.