The basic controls are: Take the controller back and swing forward, as you would a bowling ball. There are a couple button pushes to choose a spot on the lane to start the roll, and to aim for a certain direction (All one button).
You can also spin the ball. The objective of the swing is to get it to register green on the meter.
Somebody recorded a video showing how the control scheme works in the game.
My little sister was pretty good at it when we played together, and she was 6 years-old at the time.
I think it's worth it, especially now that it has trophies and online play. I still mainly play offline with people in the room, and you can play with up to 3 other people (using the same controller). Plus there are unlockable items/characters and trick shots.