My favorite execution for the Locust side includes a Locust solider ripping the arm off of an enemy player and then proceeding to beat on them with it. All lasting a lot longer than you'd think. I counted at least ten, maybe fifteen, whacks to the head with their own arm before their head exploded. So visceral, so brutal, so Gears of War.
On the other hand, my favorite execution for the Human side would be none other than the decapitation from a shield. The player runs up to a locust and kicks them over onto their back. They then proceed to ram their shield into the Locust's throat severing its head from the rest of its body in a bloody and psychotic way. I can't wait for this to hit store shelves September 20th, 2011.