Here he is doing his best Gabourey Sidibe impression.
The Book: He is described as a "small slimy creature," who is "dark as the darkness." Only his eyes stand out - large and pale. He sees in the dark with eyes that shine like lanterns. His feet are webbed, and he has six teeth. He calls himself and the ring "precious," but does not appear to have a split personality; he simply has picked up a habit of talking to himself after years of isolation. He does not cough, but instead makes a disgusting swallowing noise that sounds like "gollum."
What difference does it make? None at all. The movie version is almost exactly like the book version.
My Opinion: It's pretty hard to have anything bad to say about Andy Serkis' Gollum. The movie version not only fits with what's in the book, but adds depth and characterization that Tolkein himself never had. The "split personality" aspect of Gollum is not in The Hobbit, but it is in the trilogy (if not quite as pronounced as the movies make it out to be). I have absolutely no problem with the film showing this side of the character; it fits the scene, and keeps continuity intact. The change to the eyes is a good one, too. How is Gollum supposed to sneak around in the dark with eyes that explicitly act as lamps? How does an eye that acts as a source of light actually let one see? Peter Jackson's version makes more sense.
I was a little disappointed that Gollum's eponymous "gollum" noise was changed from a weird swallowing noise to a cough. The book's version makes him look disgusting and gross, whereas the movie just makes him look like he's got a cold or something. The swallowing noise might have sounded odd, but, that's kinda the point. That's... pretty much the only flaw I can find, here.
"I like Andy Serkis' portrayal of Gollum" may be the least controversial opinion about Lord of the Rings, ever.