I tried several of the 24-total events in the Wii and DS versions of the game. The sports are generally the same between the platforms, although a few differ. For example, only the DS has a basketball game.
In the Wii events, different characters use different motion controls. My choice of Yoshi as a swimmer, for example, required me to dog-paddle with the Wiimote and Nunchuk, while Peach uses a more traditional swimming motion.
As I flailed my arms to move Yoshi across the pool, a heart icon quickly drained. I had to hit A to take a breath and refill the gauge, adding another timing mechanic to the gameplay.
While the dog-paddle characters were the slowest -- and least interesting -- I was most impressed by the effort to make each mascot unique. Their abilities differ with each event; Sonic is faster than Mario, but the plumber has more all-around agility. Even Miis, with full arms and legs, can compete. (It was unclear how their abilities would differ from the other characters, but in the swimming events, for example, I chose the motion type.)
Many of the other Wii events I tried required some sort of shaking motion. Players get their characters at top running speed by air-drumming the controllers. (Thankfully, they stay at top speed until they encounter a hurdle or other obstacle.) Other games, like Archery, avoid this repetitive scheme.
On the DS, events also sometimes seemed too reliant on wild stylus motion. For example, I scraped the stylus rapidly to the left and right to run. (I was even concerned about how much wear the DS touch-screen could take.) But other games use the controls more creatively.
The trampoline game presents gesture arrows that players have to mimic while in the air. And a down gesture off the trampoline bounces them higher. I tried skeet shooting by tracing over escaping clay pigeons and tapping L to fire my gun. These simpler, skill-based event were more entertaining than the wild foot races. They felt well-suited to the DS.
Some DS events even skip the touch-screen. The simple table-tennis game is controlled with D-pad and button presses. And biking uses L and R to peddle, and the D-pad to steer.
The games will succeed most in events with creative controls. A few, bonus, fantasy events, like a Mario Kart-style foot-race with power-ups, add more variety to the simple mini-games. Kids may even like the games that use flailing gestures, but I hope that the final release relies mostly on precise movements. The Wii version of Mario & Sonic at the Olympic Games will be released on November 6, while the DS game is due in the beginning of 2008.