For the consecration of the elements to take place, it must be performed by a ministerial priest, whose role is different from that of the universal priesthood all believers. Since the Catholic Church, the Eastern Orthodox churches, and the other ancient Christian churches have preserved the ministerial priesthood through the apostolic succession of bishops, their Eucharist is valid.
Unfortunately, the ministerial priesthood has not been retained in Protestant churches. Most Protestant churches (all but the Anglican/Episcopalian tradition) have rejected the existence of a ministerial priesthood distinct from the universal priesthood and thus ceased to perpetuate it, breaking the apostolic succession in their circles.
It is equally unfortunate that, while many Anglicans/Episcopalians profess belief in a ministerial priesthood, the apostolic succession was ruptured in their circles, and their priesthood is no longer valid. After Henry VIII broke away from the Church, his successor, Edward VI, introduced a drastically altered and invalid version of the rite of ordination, with the result that the apostolic succession (which had previously been present in the Anglican Church) ceased, and its ministerial priesthood stopped.
This does not mean that Protestants such as Lutherans and Anglicans do not experience a real encounter with Jesus in the Eucharist. They can receive Jesus spiritually in communion, they just do not receive him in the full, sacramental manner he intended and which he wants them to experience. These communions are not just "a sham" but can be genuine spiritual encounters with Christ.
Upon entering Catholic life, one does not need to look back upon one's former communions as simply empty shams; one can view them as spiritual encounters with Christ, encounters which gave one the grace to approach Christ even more closely, finally coming to receive the fullness of the Eucharist he wanted you to have.