Several informal videos of gameplay from the E3 demo can be found here and here. Numerous details both cosmetic and mechanical can be gleamed from this footage; for example, hearts now rotate as they did back in Symphony of the Night, and if you choose to have your second character follow the character you're controlling, s/he'll teleport towards your primary character's location if they get separated.
Additionally, IGN published a brief interview with Igarashi yesterday. In it, he reveals that Michiru Yamane, the music composer behind Symphony of the Night, will be returning to compose the bulk of Portrait of Ruin's soundtrack. (She composed less than half of Dawn of Sorrow's soundtrack.) The secondary composer this time around is the renowned Yuzo Koshiro, whose past works include Streets of Rage, ActRaiser, and The Revenge of Shinobi.