What is different in Jackson's is that instead of it having already taken place in the past, where the Aragorn they see at the Council of Elrond is all ready to take his place (with his only personal fault being the breaking of the fellowship at amon hen, quickly forgotten when Gandalf returns), the transition from loner to leader is taking place before us.
Had Jackson not done that, there would be no character development in him or most of the non-hobbits at all.
Read the book again, specifically looking at the words from Elrond and Denethor on him, and in appendix A, and you'll see that transition: Denethor's Aragorn is not the one the hobbits met in Bree. Aragorn in the books has already matured to leadership, where the Aragorn in the movie is actively maturing before us.
I for one think Jackson's version works just fine, as the alternative while a good book character would be a rather flat part in a movie.
Got a "5"
Having seen TTT now, I have to followup my post here a bit. Yes, as a whole, Jackson's take on the Aragorn story is generally true to Tolkien, just bumped up to taking place during the war for the ring instead of before it...but some of the exagerations in TTT (falling off a cliff, and Arwen actually prepared to leave middle earth) i could have done without...