The Pan-orthodox Synod was raised, as ialmisry rightly said, to contrast the errors (or heresies) of the Reformed Churches. I don't agree, though, with the fact he isn't as authoritative as the others. In fact the Synod was established because of the supposed Calvinist tendencies and heretical declarations of Cyril Lucaris (Patriarch Cyril III of Alexandria and later Patriarch Cyril I of Constantinople). As Calvinist theology was technically based on contrast with Rome, many of Cyril's doctrines and innovations introduced concepts like the idea of two Sacraments in the Church or the denial of Christ's Real Presence in the Eucharist.
In order to refuse and anathemize those heresies, the Synod adopted a more... West-friendly language, even introducing the spurious concept of transubstantiation (in Greek Metousiosis) to express the Eucharistic Metabolè, and also numbered the Sacraments as seven (the same as the Roman Catholic Church).
What do I think of this Council? I consider it on the same level as other Councils held before 1056, for example the Council in Trullo. They are authoritative but not ecumenical, that means they express the position of the Orthodox on some subjects and can't be used as a "conditio sine qua non" in Ecumenical context, i.e. the possibility of a re-union with an heterodox Church should start with the analysis of the common deposit of faith (the seven Ecumenical Councils) but not the Synod of Jerusalem which reflects a particular view of Orthodoxy (or "theological opinion").
In Christ, Alex