The major difference is that Mahayana stresses altruism (conduct for benefit of others), whereas Hinayana stresses salvation for oneself. Mahayana has scriptures different from those of Hinayana, and has augmented and developed Buddhist doctrines as well. Here are a few points:
Firstly, in the Truth of Extinction of Suffering, Mahayana further maintains the possibility of “active nibbana”. According to this theory, with the extinction of the Twelve Links of Origination, it is not the dhammas arising and ceasing based on causes and conditions thatcease, but only the ignorance and moral afflictions not in conformity with Dependent Origination that are eliminated. Since “between nibbana and the temporal world, there is little difference”, upon reaching the realm of the Buddha’s perfect enlightenment, one can live beyond the cycles of the Buddha’s perfect enlightenment, one can live beyond the cycles of birth and death and never enter extinction, so one can always work ceaselessly for the cause of “glorifying the country and benefiting the sentient beings” in the conditional world, while abiding peacefully in the nibbana state anywhere at any time.
Secondly, the Theory of Dependent Origination expounds the theory that one dhamma arises all other dhammas as its conditions, and in reverse, is itself a cause for others. Thus a single person stands in relationship of homogeneity with other beings, just like the homogeneous relationship between one drop of water and the ocean. Hence the saying “All beings are my parents”, and “regard all beings as one’s only son”. This produces a heart of great loving-kindness (metta) and compassion (karuna). Metta means identifying oneself with all others’ joy and happiness, and Karuna means sympathy with others’ joy and happiness, and Karuna means sympathy with others’ grief and sorrow. With such a heart, one should indefatigably serve all beings. Mahayana Buddhism especially advocates this “pusa” (Bodisatta) outlook of life, and particularly encourages the conduct of “Six Perfections” and “Four all-embracing virtues”. (From Essentials of Buddhism: Questions and Answers)