To play the secret Scrin campaign, finish both the GDI and Nod campaigns. This will unlock the Scrin campaign of four missions. At the skirmish options menu, hold N and click you army to make NOD as ...

I think they changed it for the better, the gameplay is the fastest yet because they simplified it a LITTLE bit. Either way, i think the best in the series, though the rushing in MP is a little crazy.