The most revolutionary character in the Force Awakens....

While the character of Rey, played to perfection by Daisy Ridley, is an important step forward in terms of female representation in the Star Wars universe, aside from her gender, she is actually rather traditional in the KIND of character that she is: she is our chosen one, our Luke Skywalker,  the ordinary person who discovers that they were destined for greatness all along. Even her reluctance to embrace her destiny is part of a formula straight out of Campbell's Hero with a Thousand Faces.
There has been a recent trend among children's films (and, ultimately, that's what Star Wars is at its heart) to reject this kind of 'chosen one' narrative.

One of the best things about The Force Awakens was the way that it gave us all the familiar elements of the original trilogy while also introducing new elements. I contend that, in addition to Rey's more traditional epic hero, the film also gives us an example of this new kind of 'not-so-chosen-one' hero. I am, of course, talking about Finn. He is unique among the heroes in Star Wars films because of one simple fact: he's not particularly good at anything.

When we first meet Luke Skywalker, he is already an excellent pilot strong in the force; when we first meet Han Solo, he is a skilled smuggler and pilot who isn't afraid to shoot first and ask questions later (sorry, GL, Han shot first).  Sure, he could be cocky and reckless but, more often than not, it seems to work out in his favor. Even Leia is a tenacious, strong-willed leader who is just as good in a fight as her male companions.

When we first meet Finn, he is a stormtrooper but a completely ineffective one (granted, he's only ineffective because of his unwillingness to slaughter unarmed villagers.... still...). Later, when he frees Poe Dameron, he does so not out of bravery or moral principle but because of the simple reason that he needs a pilot and could not escape on his own.  When he first encounters Rey, he begins to rescue her from attackers before he realizes that she is a far more competent combatant than he is; shortly after this, she is successfully able to overtake him. He isn't particularly brave and his more heroic actions seem to be motivated by his fondness for Rey--- even then, his actions fall short: by the time he and Han show up she has already managed to rescue herself.  He wields a lightsaber twice in the film and loses both times (even whiny little Luke Skywalker managed to be 1-2 in lightsaber match-ups).

Of all the characters in the film, he is the one who doesn't seem to have a destiny set before him; it is up to him to figure out what his journey will be.