Judging from this video and this picture, Jack has adopted modern technology rather than relying solely on his Samurai training as he did in the past. He realizes that the only way to defeat Aku is to adapt with the tools of the time he is in rather than shun them. Jack has taken on a more ruthless approach in an attempt to return his time even if it means breaking away from tradition. He becomes proficient in using his gun and riding his bike.
Jack seems to have developed into a darker character who's kindness has faded away. He will no longer be willing to help others at the expense of his journey back to his home. From the video, i predict the original ending where Jack defeats Aku and saves his homeland from destruction was erased. Since the show was brought back for a mature audience, Genndy Tartakovosky will take advantage of it and probably make the plot more complex. Jack may ultimately have to choose between undoing the evil of Aku in his past or saving the future from total destruction.
What are your thoughts on the upcoming final season of Samurai Jack? Write them down in the comments below!