Well if you compare the amount of calories you have lost against foods you eat which are 200 calories how do you feel about it?
Its quite a low intensity workout doing steps but anything is better than nothing at all. Have you tried the hula hoop? When I use my Wii fit I try to do the steps as a warm up, then alternate between hula hoops and steps unless im bored or totally knackered!
As for whether the amount of steps you have done in the time is any good I'm not sure! But if you are putting some effort into it you should be pleased with yourself.
You dont have to stick to the rhythm they give you, speed it up but just keep it regular and you can go as fast as you like really! I turn the sound off on the wii-mote and go as fast as I want to. I find even their fastest one is quite slow.