So it's all good in theory - but early impressions of Grand Slam's implementation are mixed. There doesn't seem to be much of a problem with speed - WMP is just as alive to your input as we felt it was when we played Wii Sports Resort last July - and the game's shot selection based on the angle of your movements is correct for the majority of the time.
But directing the ball is trickier. In fact, after an hour playing around on the practice court trying to do nothing but direct the ball with WMP, I started to wonder if the unit I'd been sent was broken. At least the option to run around your backhand for a stronger forehand shot generally works - and it's no surprise to find a calories-burnt statistic in the menus given how much moving around EA wants you to do.
Tiger 10's implementation is simpler, and put paid to my grumbles about the sample WMP being broken - it certainly isn't. Clubhead direction is the main thing Tiger 10 looks for, and the on-screen clubhead indicator during your backswing is the most transparent measurement of your actions versus WMP's interpretation that you can find across the two games. Tilt the Wiimote face left or right and the clubhead twists to show how it will strike the ball at an angle. I had literally minutes of fun doing this and just observing how well it worked (check out the embedded shakycam video on this page to get a sense of the latency, which is negligible).
Twisting allows you to add draw and fade manually, rather than having to rely on claw-like multi-button grips and waggles to add depth to your followthrough. Both Grand Slam and Tiger 10 also respond appropriately to the speed of your movements, which is particularly noticeable using Tiger 10's new precision-putting technique. Presumably this is the difference between a tuning fork gyroscope and an accelerometer in action, although, er, don't quote me on that.
What you can easily say after a few hours trying both Grand Slam and Tiger 10 with and without the Wiimote, however, is that both are very promising games, but neither is a fantastic posterchild for Wii MotionPlus. Grand Slam Tennis isn't as intuitive as the abovementioned video claims, although it's certainly a good advanced option to have once you've mastered the (surprisingly deep) main game with the Wiimote alone. Tiger 10, meanwhile, didn't have much to do to improve on Tiger 09, and is cautious and conservative with its sensitive new plastic friend.
After all that waiting, then, one suspects we won't get a real sense of Wii MotionPlus's success or failure until Wii Sports Resort arrives in eight weeks' time. Although it didn't get blanket credit for it when the console launched, Nintendo's implementation of Wiimote controls in Wii Sports was applauded retrospectively for its simplicity - even restraint - and it's easy to imagine that a suite of Nintendo-authored games designed for Wii MotionPlus will attract the same plaudits, given the potential evident in EA's early attempts to take advantage of it.
Grand Slam Tennis is due out with a bundled Wii MotionPlus on 12th June, with Tiger 10 due out on 3rd July and Virtua Tennis 2009 Wii listed for June. Wii Sports Resort, also bundled with WMP, is out on 24th July.