What is wrong with Yoga? Answer : Wrong question!
The right question is, What is wrong with our understand of Yoga?
As per most people and if you ask them, they would reply Yoga means twisting, bending and turning your body in crazy ways to heal/medicinal use. Nothing would be further from the truth. Unfortunately things have come down to a level where people only give ritualistic definition of Yoga! Yoga also has many branches.
To understand Yoga in its essence I would advice you to read Swami Vivekananda's complete works.
I practice Yoga. Yoga is not a 2 hour exercise session. Yoga is a way of life. I practice Yoga, Its a branch of Yoga called Karma Yoga! So what does Karma Yoga mean? Its exemplified from a verse in Gita:
You have power to your actions only, not its outcome. Act therefore forth right without succumbing to inaction
This is to dedicate yourself towards a goal, consciously iterating and eliminating your faults in moments of self reflection improvising and not giving up until you reach your goal.
This is easier said than done! The key here is self reflection. I felt that David Allen's Getting things done took me to a better enabler to following Karma Yoga! I started following these techniques since last February.
I started taking one day a time, trying to most productive in a day. Eliminating distraction. And working towards a larger goal. The results have been astounding to me.
Karma Yoga! for westerners can be explain by a poem by Rudyard Kipling - http://en.wikipedia.org/wiki/If%E2%80%94
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If you can keep your head when all about you Are losing theirs and blaming it on you; If you can trust yourself when all men doubt you, But make allowance for their doubting too: If you can wait and not be tired by waiting, Or being lied about, don’t deal in lies, Or being hated don’t give way to hating, And yet don’t look too good, nor talk too wise;
If you can dream—and not make dreams your master; If you can think—and not make thoughts your aim, If you can meet with Triumph and Disaster And treat those two impostors just the same: If you can bear to hear the truth you’ve spoken Twisted by knaves to make a trap for fools, Or watch the things you gave your life to, broken, And stoop and build ’em up with worn-out tools;
If you can make one heap of all your winnings And risk it on one turn of pitch-and-toss, And lose, and start again at your beginnings And never breathe a word about your loss: If you can force your heart and nerve and sinew To serve your turn long after they are gone, And so hold on when there is nothing in you Except the Will which says to them: ‘Hold on!’
If you can talk with crowds and keep your virtue, Or walk with Kings—nor lose the common touch, If neither foes nor loving friends can hurt you, If all men count with you, but none too much: If you can fill the unforgiving minute With sixty seconds’ worth of distance run, Yours is the Earth and everything that’s in it, And—which is more—you’ll be a Man, my son!
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There are also other forms of Yoga! My mother practices Pranayama. Which is basically meditation and breathing practices.
You also need a good teacher. Who knows Yoga! Else you will end up making mistakes which can be dangerous.
Yoga is a way of life. Stop thinking it in terms of gym sessions.
Ultimate aim of Yoga is to make you bring you to a state of self actualization. Like what Buddha was! And healthy body plays a important role in that. So Yoga helps you build that too. But people tend to understand Yoga only as some form of medical exercises.