You would do well to pay attention to the way in which the Forest of Arden transforms many of the characters that enter it. I will respond to this excellent question by refering to the character of Oliver, as to my mind, he is a perfect example of one of the more dramatic changes. Let us remember that before he enters the Forest of Arden he is depicted as a cruel noble who has disinherited his younger brother against his father's wishes. He is set well and truly amongst the "baddies" of the play, his own relationship with Orlando eerily echoing that of the two Dukes. However, if we turn towards the end of the play, note how Oliver presents himself in Act V scene 2:
Consent with both that we may enjoy each other. It shall be to your good, for my father's house and all the revenue that was old Sir Rowland's will I estate upon you, and here live and die a shepherd.
Note the dramatic u-turn that Oliver has undergone. Here he is freely bestowing the wealth that he once hoarded so jealously upon his brother and freely giving it all away so that he can marry Celia and live in the countryside. His time in the Forest has obviously taught him some harsh truths about his own life and how he has been living it up until this stage. Going to the Forest has changed him dramatically and shown him for the character who he really is.