I have seen all 3 of his films repeatedly.
While I tink film historians/critics overrate him a bit saying he was THE voice and actor of his generation, etc.
He was indeed a fine actor for the 3 films he did.
East Of Eden & Rebel Without A Cause both show his range at teen angst, melencholy, rebellion, disillusionment with his parents.
Giant..actually in some ways is my favorite. Because he tried to show his range as more than the angst driven rebellious teen. The scene where Liz Taylor as Leslie visits him in his little desert shack, and you knwo how very much in love with her he is..but he knows she not only is married to Bic (Rock Hudson), but that she is a sophisticated, educated lady out of his league...is so expressive...when he offers her coffee...then realizes..she drinks tea.
He has only a few dirty dishes in his messy little shack..but it means so much to him to try to find a little cup & saucer and make her a cup of tea...
Also, when he plays the Aging Jet, sitting alone at the honorary banquet table, rambling on in drunken incoherence to himself about how much he loves Leslie...and her daughter, Luz (Carroll Baker), who has a crush on Jet..is listening at the door and overhears him...and she is as crushed..as JET is about never requiting his love for Leslie.
His best scene in East of Eden (since you said you haven't yet seen it I won't spoil it), I will just say...is the end...his relationship and words first with Julie Harris (his brother's fiancee, but who loves Cal (Dean) and he her)..
...and especially for his father at the very end of the film. Subtle..yet you understand...the feeling and emotion that is meant to be conveyed.