Main writer was first-timer Jade Halley Bartlett, followed by extensive rewrite by Michael Waldron (head writer and EP on Loki). People will have views on whether that's good or bad, but Gryffindor Grumblecrotch and others have said it's been a much more collaborative process with the actors and director than the other Marvel movies. That was evident on Loki and is kind of a Raimi hallmark as well.
They are also going for an actual horror vibe: Raimi kinda has the chops for that. Also not known for happy endings, so this might not resolve itself in one flick.
Mordo did feel a little underused in the tail end of the Strange movie, fabulously smarmy-evil post-credits aside. I hope he's got more to do this time around, but it's a very busy movie already with Wanda and America Chavez thrown in the mix.
Just for once, not going to speculate on who the Big Bad is - they're teasing Ultimate Strange, Wanda, Mordo, and even Strange himself. They could also be hiding Kang. but given there's the possibility of mirror universe/alternate universe/illusory versions of anyone showing up (including Wong - maybe even Bruce,Tasha, Cap or Tony), all bets are off.
And not knowing what the heck actually could happen feels good. Been a long damn time.