I really liked the 2 sirens storyline that they showed in ep 4. At first Sybil felt like a very average.. mehh.. kinda villain but this Seline is pretty crazy. I don't know how strong Cade, the Devil, will be but he doesn't look very intimidating as of now.
Also I feel (wish/hope) Katherine will be back. The way Georgie was dragged into hell was quite similar to the way Katherine was dragged into God-knows-where in season 5.
Me too. She was one of my fav badass characters back in the earlier seasons. If Nina comes back to film the finale of the final season, I would prefer her to be back as Katherine rather than Elena. :D