I agree that all the actors gave excellent performances with the roles they were given. However, many of the movie characters were significantly different in personality and motivation from the characters Tolkien created - some so much so that they were different people with the same names.
How much one is bothered by the alterations of plot and character made by Peter Jackson is, of course, a personal matter. It bothered me a lot!
Faramir is the one that bugs me the most. The extended editions made him a little closer to how he really is in the books...but only a little.
Don't forget, that Frodo had the ring since he was of age, and it had stopped Bilbo's aging.
So, Frodo should look young as well.