They just took away all his good lines. Imagine movie Frodo laying down the law to Gollum:

In the last need, Sméagol, I should put on the Precious; and the Precious mastered you long ago. If I, wearing it, were to command you, you would obey, even if it were to leap from a precipice or to cast yourself into the fire. And such would be my command. So have a care, Sméagol!

I think if they had gone with the wise and courageous Frodo from the books then Elijah Wood would have been better at delivering this sort of line than Martin Freeman.