An interesting variation might be to drop a skull where the fragged player was (or you just harvest their corpse).
Just like
Greed actually is. Without the Titans, Vehicles, and extra-gametype related things, of course.
I tried it with bots and I'm sure I don't get it.
There was some skulls, and when I pick they up, they didn't give the team point. What are the rules?
Well, it still better than Overlord, because it doesn't work with bots....
Look at
this video @ 0:35 to get an idea on how to play. Basically, as sago pointed, you frag someone, a skull appears on the skull generator at the middle area, (or where it's placed) then you collect that skull, go to the enemy base, and touch the skull pod to score.
There's a Harvester video, but it's useless, since he collect skulls but don't put them in the enemy skull pod.
I also suggest you to play with the latest
OAX, since it fixes most things about many things.
(BTW, Quad Damage is one of my fav songs from SM, more than some of my fav tracks from Q2 OST)