I have NO idea what this is. Geoff said on-stage it's a co-op action adventure game, so this doesn't seem like a sequel, but more like a standalone DLC? This re-uses a lot of enemies and assets from the original, and even Nameless King from DS3 is here.
To answer the OP, it's an expandalone with flight mechanics and new powers. Regular Elden Ring is also a co-op action adventure game, but more notably in this trailer is that none of the other players are phantoms, meaning that, like they said in a previous interview, the "seamless co-op" mod and its popularity has influenced how they're handling multiplayer going forward.
My big question is whether this can be played singleplayer or if it's designed from the ground up to be multiplayer, since the trailer put a lot of focus on it being co-op. Man, I'm hyped either way!