To me, the worst twist was the passenger, first supposed to be an objet, only to turn out to be Sydney's half sister.
The very notion that Sloane, became obsessed with Rambaldi only to find out 25 years later that he had fathered the perfect conduit to Rambaldi, aka the passenger is so lame, it's so ridiculous !
Stupid as well is the notion that Irina Derevko has a child with a guy she obviously can't stand, what are we supposed to believe : that she forgot her birth control on the very night she was supposed to get intel from Sloane through sex ? She looks like an idiot, and Sloane, by cheating on Emily, loses his only redeeming feature : he was supposed to be a good husband.
Finally, the way they dealt with Nadia, using once again the same plot : a lonely girl, who thinks she's working for the good guys is in fact tricked into working for the bad guys, honestly, how many times do we have to go through the same story again and again ? Then the passenger is defeated by a coffee table ? The only godd thing about Nadia's death is that it's consistent with the rest of her story : completely lame