Rollo has a locket, this locket seems to have the power to temporarily erase memories because at the scene where Kallen gets knocked out, she looks as though she didn't know what just happen. Before this scene, we see the locket fly by telling us it was the locket.
We also see it in the OP.
The Emperor and V.V are linked. They probably made a contract together. The Emperor also sent V.V to destroy Lelouch's plan by abducting Nunally.
Also, we can tell Nunally has been kidnapped. However, Lelouch forgot about this due to his 'fake' memories, he may well remember Nunally on the next episode, after all, without her there's no point of the battle. We also see her in the OP with a 'royal' wheelchair and she's dressed quite royally too. There's a good chance the memories of everyone else who knew Nunally were messed with since they can't just forget about her like that.
Rollo probably used his 'power' to erase people's memories, he doesn't have the geass but rather the locket. That way he could've inserted himself into Lelouch's life. So Rollo is a fake brother who is just observing Lelouch. (he could even be V.V in a different form but lets no go that far xD) He may be the one behind erasing the students' memories of Nunally too.
Rollo also has a dark side as we saw on one of the trailers.
From the OP ^. Emperor has the geass. Could be the same as Lelouch's but I'm guessing an 'all-seeing' type since he seems to know everything that's going on without leaving his throne. He's clearly linked to everything that's happening, we even see him in one of those visions in Season 1 where he's in some sort of place linked to C.C's clan.
C.C can talk to Marriane as we heard in Season 1, she must have known Marrian as
we see her at the start of Season 1 'observing' Lelouch and Suzaku.
Orange-kun is back as seen in the OP.
Suzaku is a bastard as always.
Villeta is a P.E teacher probably to keep track of Lelouch.
A lot of poeple seem to know that Lelouch is Zero now which is kinda lame...
Well, the old Lelouch is back now, can't wait for Turn 2.