I've finished Command & Conquer 3: Kane's Wrath. I like the game - but I'm disappointed that they didn't address most of the question marks left behind by C&C3 Tiberium Wars. All we get is that tidbit at the end where GDI has apparently wiped NOD off the face of the Earth. No news about the Scrin or Kane's journey through the threshold. Unfortunately, I can't recommend that you buy Kane's Wrath, since while it does fill some back story, it doesn't further the story at all, and is more of the same C&C3 gameplay.
I'm recategorising loads of stuff - and finally removing my archaic rule of having only one category per post if at all possible.