The estates/tax system.
I used to be enthused by it, and it brought a whole new RP dimension... but the old centralized taxes was the foundation of any team ethos. It also made for more effective war machines and faster recovery, as any region or production loss would take a little gold off everyone instead of a lot off a few, and it was much easier to put the funds where they were needed instead of having the wealthy regions give all of their wealth to an inactive (or non-fighting) few.
