The trailer includes some very pretty CG footage (as is the norm for Square-Enix) of some rocks rising out of an ocean with storm clouds above. A ray of light shines through, illuminating a standing figure on one of the stones - the Warrior of Light. Cue some gameplay footage, showing the Warrior of Light, Garland, Zidane and Kuja. The latter two can both be seen going into Trance mode during the battle. Movement seems fairly unrestricted, as the characters are all flying around the levels quite effortlessly. The trailer ends with more CG footage, as the Warrior of Light watches the ground split apart, spewing lava into the air. Sephiroth steps out of the molten waterfall and gives us the look. You know. The look.
Exciting stuff, by all accounts. Though there's no new information as this is almost certainly what was shown at the Square-Enix Party. Though it's curious that Square-Enix would hide it away in the member's only area. We'll keep you up to date on any developments.
[Update] Trailer has been embedded, courtesy of Jeux-France.