Imaro said:
You can play the traditional, adventuring party type fantasy or you can play the leaders of a mercenary band (where there are rules that are elegant and easily grasped for followers), or even the ruling a kingdom level where, again there are rules that take it to a level where you can actually control and maneuver the soldiers, land, wealth, spies, etc. that you control.
As the guy who wrote the Affiliations chapter in the PHB II for D&D 3.5, I was very interested in Reign. I think this sort of play is missing from traditional RPGs. I've run a lot of campaigns over the years, and in every one so far, at least at some point, I needed rules for large-scale organizations to act. War, taxes, declaring holidays, espionage, ruining economies, that sort of thing.
One big difference: in Reign, the emphasis is on the players all banding together to form one company. For example, all the players are pirates, and their company is a pirate ship. In the PHB II, every player could join whatever sort of affiliation he wished. A cleric might be affiliated with his church, while a rogue is associated with a thieves' guild.
A great advantage to company or organization play is that the organization can become the focus of the campaign. Player death can be meaningful but not the stumbling block it is for certain players: now they can be more invested in the company than in their character.
The game I'm working on now includes company play and goes a few steps further. Players with a military company can recruit and train multiple different units to wage war. Players with a shadow company can dispatch assassins, steal tax shipments, run cons that topple kingdoms, etc. And there's player-vs.-player company potential, and multiple company potential... Well, I'll stop plugging now.

The point is that Reign does a good job, in my opinion, of opening up an area of play that I've always wanted to see RPGs develop.