I've had a few hours to play with Wii Fit now and my initial impressions are pretty positive. I'm 6'2" myself and haven't noticed any problems outside of my feet not quite fitting onto the balance board. I can't imagine that too many people out there wear a 13 1/2 shoe though (or bigger, UncleBob, you sasquatch!). I can't say that I felt the BMI to be very fair toward my fiancee however. It's obviously not a very accurate system anyway, but there's no way it was right about her. She has a wider frame than your typical woman from a commercial. It's not fat, just general build. That said, it's guesstimate seemed pretty on par when gauging me.
I think that the game would have been better off if it actually did something to help you achieve the goals that you set. It could set up a routine or suggest certain exercises pretty easily, but it doesn't. Furthermore, it seems that the only way to mark off a day is to weigh in. I don't think that weighing ones self every day is beneficial, as your weight will fluctuate from day to day. Perhaps once a week would have been better, with the "I played today" stamp requiring some activity instead.
Though perhaps a little beyond the scope of the game, it would have been nice to see a calorie counter added. You could input what food you ate throughout the day and get a sense of what your nutritional intake is. Likewise, you could input an estimate of any exercise outside of Wii Fit. Using this, the game could further offer more customized routines. There are plenty of websites and diet programs that do this, such as Spark People .
Graphically, the game is very clean. With so little going on however, I find the noticeable jaggies to be somewhat disappointing when looking at the Balance Board caricature and such. Also, why don't the trainers' mouths move when speaking? That alone throws things off a bit.