He was always far more reserved than Bilbo, as far back as I remember him. But still as a young Hobbit he could and did laugh freely, his humor perhaps the more delightful because his many griefs experienced gave it depth. He was always compassionate and intelligent, but with a level of impatience with the slowness of others to appreciate the depths of their own lack of experience.
Frodo Baggins was never a simple Hobbit, and now he is so changed by his time of trial with the Ring. If he remains a Hobbit at all, it is merely due to the accident of birth. He offered himself due to imperfect knowledge of what the Ring would do if left abroad within the wide world and a terror even then of losing It to another. Although It was just awakening, yet It still had such a hold upon him! Even after he realized he would not likely survive the destruction of the thing, and his further appreciation that the only way he could even see It destroyed would be for himself to fall with It into the fire, yet he persevered, in the end so scoured that he truly did not mind the realization that he must die himself to see the quest achieved, as he desired only rest and freedom from Its torment there at the end. He was disappointed to wake to the realization that he was yet alive within this world, I think.
What griefs he has known since, the worst being the realization that he has no further place within the world as he found it. He looked into the heart of Saruman, seeing what he had been intended to be, and recognizing another whose very being had been scoured away by the lust engendered by the Ring, and he knew pity. He was granted no wife, no child of his body and spirit, no new family to replace that stolen from him when he was but a child. He received little honor and less understanding from his own people for all he had sacrificed for them.
That was the worst, I suspect--that sacrifice of his identity as a Hobbit of the Shire.
So, come my friend--come now and know the final act of transformation. Realize now that if you have lost yourself as a Hobbit of the Shire and a mere mortal from Middle Earth, it is merely the prelude to finding yourself as you are now capable of being. There is still so much for you to know, and to do, and to be....