Although I like it better, COE has tons of problems. The way all the countries in the world agree is totally unrealistic. They would have turned on each other demanding that countries with a weaker military hand over their kids. Also, nobody puts up a fight or tries to come up with an alternate solution rather than just handing the kis over except Torchwood. There's no way all the countires of the would would act unilaterly and not pursue a military option. Since they made a point of showing that the 456 were adapate at viruses, it would have been better if they released a virus on earth that only they had a cure for. Then, I would get not trying for a military option because they would need the 456 alive for the cure. Of course, the resolution would have to have been different for how to defeat them, and there'd be no Stephen sacrifice.
Even though I didn't like MD, Immortal Sins is one of my all time favorite episodes even though I complaing about Gwen's mishandling of the kidnapping.