The thing I liked about the Killzone demo was that Far Cry 3-style death from above chained into a thrown knife kill. That's one of my favorite things about Far Cry 3. I don't know if Killzone 3 had that, but if more games have takedown systems like that, that's good news for me.
Once they talked about being able to record footage, spectate/stream gameplay, briefly take control of someone else's game, and streaming games from the store, I didn't care about what they talked about next. I'm already sold. I don't even care. I was just hoping for cross-game chat, but they gave me that and quite a bit more.