In terms of being historically accurate, it was for the most part. The characters were real people, and while Hollywood might have dressed up their abilities and personalities for the screen, and hired two superstars to play Woodward and Bernstein, that does not change the accuracy of the events that took place.
Given that the identity of the source for Watergate information, nicknamed Deep Throat, was a secret until very recently, they had to be creative on that score and they were, a bit.
Not sure how the film could be "balanced". How could it show the Watergate scandal from the Nixon Administration's point of view, given that it did happen, and that their actions were indefensible? It's like saying Schindler's List was imbalanced. OK, not a perfect example, but you get my point.