Because of a long-standing hatred of Dark Eldar, my aforementioned opponent, who used Grey Knights rather than normal Marines, fought against my Guard instead. And I was thrashed. His list was essentially:
Psybolts on everything...
Mine was my usual Guard fare: Yarrick, CCS, 4 Vet squads, one in a Valk, one in a Chimmy, two Sentinels, 20 Ratlings, Marbo, a Russ and some allied ISTs in a Rhino.
The entire army was essentially tabled after Turn 3 after my failure to realise his Puries were in the 'Raven and his big Termie squad having Scouts lost me my Ratlings on Turn 1. After this he essentially closed in on my castle and mopped everything up gradually, with two of my three Demo Charges being worthless and Marbo's being too little, too late. How can 28 models be so damn good? At least with DE I might have been able to fight back! And the Dreadknight with personal teleporter...feth, I needed poison then, but all my Ratlings died in one swoop...
It's safe to say that I didn't really enjoy that much. So next time it's out with the rusty Guard, and back in with the Kabalites so I can fight properly again.