The fact he said a few things that deeply disturbed the people of his congregation (who quite clearly once loved his teaching) enough to get rid of him implies it must have been pretty far from or contradictory of the New Testament teaching.
It is not clear that he was dumped. And while I am certain that there were people in his church that wanted him fired, the board of elders did not say he was fired.
Below is a pretty good analysis of the issues in his book. Yes it is controversial and goes beyond what many people believe about Hell, but he continues to deny that he ever said there was no Hell.
http://www.christianitytoday.com/ct/2011/marchweb-only/rob-bell-universalism.html?start=1
Essentially what he said was that everybody makes it to Heaven. That even after one dies God continues to shower his love on them to such an extent that even the hardest, most evid heart eventually succombs to such love and finally embraces God, thus saving them. Universalism.