I'm disappointed with the amount that they left hanging, but you are right about the smooth way they brought in Ella. That was very clever- no show has done that before. The fact that Ella actually killed Cassie also added to the air about the show that they are telling a story that has been in the planning from the beginning, and not succumbing to the wants of the actors who play the characters.
They make everything look like that is how they intended it to happen all along.
Still, as much as I love Ella, I think it would have been interesting to see Cassie's powers develop as she tried to take out Azazeal, Jez, the remainder of the Nephilim and ultimately Malachi.
Totally agree...even if the show wasn't intended to end there by the writers it still ended there and it still aggrevated me that it ended that way. I find it interesting that the young lady who played Cassie was allowed to leave mid-season like that...didn't she have a contract? I did like the Ella character, too, but I just liked Cassie better. Oh well, c'est la vie.