Of course, portraying God on film always stirs up some controversy. It becomes hard to separate the fictionalized character being depicted in a story from the preconceptions of believers of various faiths who might view it as sacreligious.
Amid the cries of "Blasphemy!" from those who feel their Creator is being mocked or marginalized, there is the practical challenge of bringing to life an idea that has no corporal presence, a notion of perfection that when portrayed by an actor automatically carries an assortment of imperfections. In some religions, any attempt to "re-create" the Almighty, or even say or write His/Her/Its name, is sinful idolatry or heresy.
George Burns pulled it off nicely for three movies in the original Oh God! series, but even he faced criticism. Others have also portrayed the Supreme Being in various films. Morgan Freeman in Bruce Almighty and Evan Almighty and Alanis Morissette in Dogma and Jay and Silent Bob Strike Back are the most notable that spring to mind. (I've been told that James Garner also played the part in God, the Devil, and Bob, but I've never seen that movie.)
Some have only played the voice of God, such as Val Kilmer in Prince of Egypt, Trey Parker in South Park, Donald Hayne and Charlton Heston in The Ten Commandments, Graham Chapman in Monty Python and the Holy Grail, and Harry Shearer in The Simpsons.
Sometimes, it is not stated outright that the character is supposed to be God, but it is still rather obvious. Examples include Whoopie Goldberg in It's a Very Merry Muppet Christmas Movie, Ralph Richardson in The Time Bandits, John Huston in The Bible, and Charlton Heston in Almost an Angel.
I think a seriocomic update of Oh God! could not have come at a better time. I hope the film respectfully explores some of the many issues in society in which the name of God has been invoked, 99.9% of the time to justify questionable human actions. Sometimes through humor the greatest truths can be discovered. Betty White is certainly an interesting choice for the part.