In Buddhism, existentialism is in fact quite important. Existence of beings or individuals is the cycle of birth and death. You exist in a specific physical realm, or a specific psychological state, from which you transcend, through Buddhism, to the next.
The goal of Buddhism is to liberate oneself from this realm of existence, through rebirth and reincarnation - into Nirvana.
Though similar in concept, the end goal is different in Buddhism and Hinduism - Nirvana, respectively communion with the divine.