How and why does obama doing a good job this year?

This is, of course, a matter of pure personal
opinion.

I think that you can, if you believe in this, say
that Obama has done a good job by pushing the health care reform bill through Congress. 
It had looked like the bill might be dead when Scott Brown won the election in
Massacusetts last year.

Other than that, there has not been
much going on.  The health care bill took up most of Obama's time and
energy.

You could say that the economy is starting to turn
around and you could give him credit for that, too, if you want
to.