Take Donkey Kong, one of Nintendo's biggest stars (designed by a young Shigeru Myamoto, the creator of Mario, in his first ever game), chuck in a rythym game and what do you get? Donkey Konga – a music rythym game with more than a sprinkling of Nintendo magic.
It comes with its own special controller (the konga drums – you can buy more for multiplayer or just let the others use normal controllers like the plebs they are) which detects your beats (on the drums) and even when you clap – all of which ties into the on-screen action; hopefully in line with the beat.
It's great fun, easy to learn and approachable to all. There's a huge variety of recognisable tunes in there (from Nintendo classics through to classical and pop music – none of which, unfortunately, is by the original artists) and the interface is so simple that anyone can get it: hit either the left side of the drums, the right side, both sides at once or clap. That's it. Easy to learn but tough to master – there's enough variety in both tunes and difficulty to keep you slapping and clapping until the sequel comes out.
The only real beef with it is that it's hard to keep the controller on your lap; as you hit it and let it go, it tends to move around a bit. Once you master that, you'll have no problems. I recommend it!