To train the animators, the team [at Blue Sky Studios] created a three-week crash course on the style that they dubbed Van Pelt University (after character Lucy van Pelt). That started with drawing Charlie Brown — which proved much tougher than many expected — and watching and rewatching the classic animated specials, including A Charlie Brown Christmas (which marks its 50th anniversary in December). A style guide informed details, including eye- and nose-direction charts.
Food was used for references. For instance, a side view of a foot was the shape of a baguette, while the bottom of the foot had more of an egg shape. This vocabulary also informed production design, with clouds in the sky resembling popcorn.
"It had to feel like you were looking at the strip, with the spontaneity [of drawing]," said art director Nash Dunnigan of the production design. “We also achieved a nice level of simplicity, so nothing overpowered the characters.” ...
I've heard varied reactions about the success of the CG images of Charlie Brown and his posse. The proof will be how the movie-going public responds to the movie when it rolls out this Fall.
If the Charlie Brown Movie is a hit, little else will matter.