The game in your picture looks more similar to the dancing games. The Wii balance board is maybe 1' x 2'. Some of the games involve stepping on and off the board, but most of them are done with the feet planted. The pressure sensors are very sensitive, so they either tell you where your center of gravity is located (in the tests and exercises), or have you shift your center of gravity to manipulate on-screen objects (in the balance games, including many of the Training Plus games).

I think it's a terrific way to work on proprioception and balance. As for cardio, it might be good for someone coming off the couch, but not for anyone with even minimal cardiovascular fitness.

Some of the balance games are really fun, and there are a few third-party games that take advantage of the balance board (Kororinpa, Raving Rabbids TV Party, and a couple of snowboarding and boxing games). Many of the exercises in the "strength" category involve balance as well. I do a few of the Yoga poses now and then, but I'm not really a fan of Wii-style Yoga.

I'd buy one again just for the Table Tilt games.