Well I agree that Killzone does look very good, the weapons look pretty solid and meaty to use, but I still think there is a bit too much grey in there.
As for what Resistance is missing... I think there is something missing too but not sure either. I think it might actually be the weight of the weapons, because when you shoot, your gun doesn't feel all that powerful and so when you kill an enemy it can seem unsatisfying.
But hey, it is so much fun when you're on a roll.