Considering that you get a trophy for watching that video in GOW1, it means his brother is an important character in the whole GOW universe. In GOWIII you see some notes written by the "other" critizicing why, while he is in Hades, kratos becomes a GOD.
Also if you check the ending in CHAINS OF OLYMPUS; Athena also refers Kratos and the "other" as they. Who could be as important as Kratos if not his brother?
SPOILER: GOW:COO ENDING
I think the devs have already the next story plot for the series, but they aren´t saying a thing because they obviously dont want to spoil the game for you.
Most probably the "spartansstandtall" website is about the next PSP GOW game, and with it some more clues about the "other".......First day buy for me!! XD.
