I assume you haven't seen the movie in 10 years or so.
The movie is told from his perspective, and he is the catalyst for Luke's arc in the originals. Qui Gon was the original "rebel".
The Republic crumbled, as did the Jedi order, in the prequels because they were rigid and emotionless. Yoda and the rest of the order were wrong in trying to separate emotion from action. This pushed Anakin away and towards Palpatine.
Luke triumphed over Vader and the Emperor by tapping into his emotion, and forcing Vader to re-tap back into his. It wasn't just a triumph of good versus evil, it was a triumph of the silly notion the Jedi were putting forth in the prequels. The notion that lead to their own demise. The notion that Qui Gon didn't agree with or adhere to.
The first scene with Qui Gon in it he is telling Obiwan that Yoda is full of shit and to ignore what Yoda had told him. As he meets with the Gungans and those on Tatooine he uses his force powers to manipulate people that pose no credible threat to him. He gambles and cheats. Away from the reaches of the Jedi order he plays by his own rules and lets his feelings guide him. There are a few points in the movie where he advises others to trust their feelings, and gives advice based on his feelings.
Qui Gon is no mystery character. He was the best Jedi the order had seen until Luke came along and used the same principles to defeat the empire.