I think it should be a high drop character with a devastating effect. Only it should be realy slow about getting it. They have always been pretty good about matching powers to the actual characters in the comics, so that would be about right for Galactus.
I mean, he's the sole survivor from the Universe that existed before this one, consumes whole planets to sustain his immesurable power, but it takes him longer then the line at Mission:Space to set the dinner table.
So a great power, with a delaying drawback would be just about right.