I like Warhammer Ancients Battles, but I don't know if those rules really could give a good simulation of the command problems the French were facing at the battle. With WAB, you can adjust the Leadership values of the troops and include scenario rules, but I suspect the battle would just have the French pushing their men-at-arms across an open field while the English fire at them. Turn 1, French move 3". English shoot. Turn 2, French move 3". English shoot. Etc. Eventually, the French would arrive, and then you'd roll some Break tests after melee. Hmmm.
Piquet has a very different approach to gaming than the traditional "You go, I go" pace of WAB. Each army has a Sequence Deck that is tailor-made to its capabilities. The players roll against each other for Initiative with d20's and the winner gets to use the die roll difference worth of Impetus Pips (IP) to activate his deck. It costs 1 IP to flip a card face up. Once face up, it costs 1 IP to use the card. For example, the Infantry in Open Move card, allows the player to move one infantry unit or Command Group per 1 IP spent. Firing a unit costs 1 IP. The Reload card allows you to reload one missile unit per 1 IP. You don't like the card? Flip another one for 1 IP.
There is also a mechanism for saving some Impetus Pips to use for Opportunity firing and actions during the other player's move, so you don't have to sit there and just get your ass kicked.
There are a variety of cards in the decks. The English have better cards, like the Brilliant Leader card (which can be used as any other card), St. Crispin's Day Speech, and Crushing Missilery. The French have bad cards like Milling Around, Apprehensive Levy, and Uncontrolled Charge.
The nice thing about the rules is you never really know what is going to come up in the deck. You can never count on getting the cards you need and you never know how many Impetus Pips you're going to have from turn to turn. The English might get tons of Reload cards and hammer the French with arrows while the French are Milling Around in the muddy field. Or maybe the French can get extremely lucky, roll tons of Impetus Pips, and Infantry Move their dismounted knights over and over again across the battlefield.
Each army has a reservoir of Morale Chips that reflects its general will to fight. As bad things happen, like destroyed units, routing units, etc., the player loses Morale Chips. The player can also spend Morale Chips to rally units, re-roll morale checks, or force his opponent's units to take morale checks. Once a player runs out of Morale Chips, the future of his army is bleak.
The Band of Brothers supplement for Piquet gives some great background and flavor to the Piquet Master rules. (The Master rules are available for something like $5. You need both the Master rules and a Supplement to play).
At Agincourt, the English longbowmen use stakes and have Volley Fire capability. The stakes stop mounted units, forcing them to use 2 Move cards to engage the archers. Volley Fire allows them to aim high, increase their long range, ignore linear obstacles, and rain arrows on the French with a reduction in damage capability. Missile troops can also fire versus the armor of the horses of mounted troops instead of their riders, so you begin to understand why the French knights dismounted and trudged toward the English.
The rules also allow for variable quality between units before the battle. Before each battle, you roll to see if the unit is motivated, average, or weary, and this effects its fighting ability in the game. A very cool technique is to wait until the unit has to make a roll before you determine this quality. "Aaaargh, my retinue knights are vacillating!"
The Agincourt battle matches up a Late French HYW army against a Late English HYW army. There must be over a hundred army lists in the BoB supplement and I obviously have focused on the Hundred Years War. Each list has a basic list of 12 units you can use, but there is also a special muster section called Beat the Drum which allows you to buy other units, develop intelligence, dig a hidden ditch, have a guide lead you through difficult terrain, invest in training and metallurgy, and otherwise customize your armies before a battle. Very fun.
So, the plan is to try the battle with Piquet: Band of Brothers. I'm still basing the miniatures individually for WAB, but since Piquet is stand-based, I can use magnetic bases and metal Piquet stands and still use my figures for both rulesets. Once we try Piquet, perhaps we'll try it with WAB and compare the two games.