[Galadriel55]

I think that Frodo was never exactly an ordinary happy-go-lucky hobbit. Maybe he was in his childhood, but we don't know too much about him in that stage of his life as a character.

Even before he got the Ring, he was more thoughful and perhaps more "deep"* than other hobbits. He learned Elvish from Bilbo. However, the change in him is still enourmous: before the story of the Ring he still felt himself a part of the Shire, and the Shire - a part of him.

I'd say that Frodo changed more than Bilbo did. Although he left partially because Bilbo left as well (so Bilbo had the bigger bulk here), the end result was different. Bilbo as learned in Elvish lore, but he was still a fully-fledged hobbit inside. Frodo was less learned, but he was less of a hobbit inside by the end of the Trilogy. In a way Bilbo is the Elvish hobbit, and Frodo is the hobbitish Elf.


*By that I don't mean to say that other hobbit characters are shallow; he was just less down-to-earth/simple.