The coolest I've been involved were run with three people participating.
It was a tactical (platoon level) WWII game, run by an umpire. I commanded the British and a friend the Germans.
The umpire provided each player his OOB, objective(s), a picture of the table (6' x 4', before the troops were placed), and a gridded map with simple coordinates (A1 through G12, or some such).
Before the game started, we commanders provided an overall scheme of maneuver, with initial positions, to the umpire (I.e., 1st Squad and MG are base if fire near B4, PC and second squad are assault element, jumping off from A2, towards house at E9, Plt Sgt, PIAT, and 3rd Squad off table in reserve).
With that, the umpire played out Turn 1. Then he sent each of us a tailored write up, with pictures, all based on your force's perspective, so we players only knew what our troops knew, saw only what our troops saw. Based off those reports, we would then provide written orders to the umpire, then he would carry out the next turn.
We played two games like that, and they were fantastic. For the first we used Chain of Command, a great set of rules, but a set which (because of the command mechanisms) has quite a bit of friction built into them. We found that is normally fantastic, but was a bit too much for PBEM, where we were already generating plenty of friction, and a lot of work for the umpire. For the second fight we used Bolt Action, which made the action flow more smoothly.
From my standpoint, the big difference was that Bolt Action allows every unit to do something every turn, which helped the pace move along and simplified the umpire's job. Even trying to set priority of action in our written orders, the Chain of Command dicing mechanism allows for so much variance that we were unable to communicate to the umpire in a timely and coherent fashion for him to not find himself making decisions (in terms of which units to activate, based on the die rolls) on our behalf.
We even tried having him roll the next turn's command dice and including those in the previous turn's write up, but it didn't really do much to streamline things, it really just drove a ton more information requests to the umpire, which drastically slowed the pace of the game (at best we were doing one turn per week).
I think Chain of Command is great, it was just too much for us, not being there to see the table, then make our decisions and carry them out. Bolt Action's simplicity worked better because each player simply took a roster of his forces and assigned everyone a task, I.e., 1st Squad fire on enemy unit at F7, 2nd Squad move to G4, etc…
I hope that helps, let me know if you've got any questions.
V/R,
Jack
