When I bought and watched One Son, I imagined that there could be no episode better than this. The plot was so exciting and revealing, with so many of the questions answered. This had to be perfection...and then I saw Biogenesis.
This video was so good that it rivalled One Son in almost every way. It didn't answer as many questions as the former, but it did pose entirely new ones: who does Krycek really work for? Did the aliens create life on Earth? Are CSM and Mulder's mum psychic, like Mulder was for a short while? That said, we finally know who Mulder's father is...unless he's lying. And lots of people die.
My all-time favourite scene has to be either when Scully finds the buried craft, or when it disappears, or the vision of the apocalyptic future, or...there are loads!
To round off, these episodes are the joint greatest ever! Keep going with these plotlines!