Some of the stuff on the wii fit/sport discs are still fun – like the one with the penguin that has to balance and slide across the mini-iceberg to catch the jumping fish – a favorite of the wifes…
The original tennis is also still fun – just play it more like a table tennis stroke rather than a full tennis stroke as it is more timing based and with a full stroke but nothing to ‘hit’ against you are inviting an rsi type injury.
The more advanced tennis games with the improved motion controller seem to be a little less ‘realistic’ and the controller actions required are a bit too violent to safely avoid injury and don’t bare much resemblance to an actual tennis stoke.