Nichiren says follow the Law, SGI follows the person.
Nichiren teaches the Treasure of the Buddha and the person [subject] of the Secret Law of the Object of Worship is Shakyamuni Buddha and SGI states, it is Nichiren.
Nichiren teaches that the Transmission of the Law is through faith in the scrolls of the Lotus Sutra [the Gohonzon and the Lotus Sutra itself] and SGI teaches that it is through the Three Presidents and the SGI itself.
The prime point of the Lotus Sutra, according to Nichiren Daishonin, are the Three Treasures and Three Great Secret Laws. According to the SGI it is the Mentor-Disciple relationship.
The Buddha and Nichiren teach that there are no distinctions among the disciples and believers of the Lotus Sutra but SGI is an authoritarian pyramidal structured hierarchy.
The SGI teaches Interfaith. Nichiren teaches the exclusive faith and practice of the Lotus Sutra and the inferiority of both provisional Buddhist teachings and non-Buddhist teachings.
Nichiren teaches that faith is first and foremost. The SGI teaches that practice is first and foremost.
The SGI teaches that one can believe in just about anything as long as one chants the Daimoku. Nichiren teaches to only believe in the Lotus Sutra.
Nichiren revered and praised Shakyamuni Buddha. SGI reveres and praises Ikeda and themselves.