I haven't been experiencing tech issues with Xbox Fitness (just started though). I am missing Nike Fitness however. I liked having one personal trainer and frequent fitness tests--it felt like a more complete and tailored-to-me experience. I'm also not into the "fitness personalities" and all their motivational shouting that Xbox Fitness offers and would be into a more low key and cooler/hipper approach. Xbox Fitness just feels like fitness DVDs with a slightly better experience. Yoga would be great too.
I'm hoping that Xbox sticks with this though and I will continue to support it as working out this way is the most efficient way for me given my ridiculous schedule.