In the last session of my 4E Dungeons & Dragons campaign the players led the rebel army in a battle against the Iron Circle mercenaries who had taken control of the Barony of Harkenwold. While I did run this battle somewhat differently than written in the module, I kept the basic idea to have the actual battle take place behind stage, and "simulate" the participation of the players in that battle through a series of three skirmishes. Two of these happened in the last session, and this session thus started with the third and final skirmish, pitting the players against the enemy general.
The battle started somewhat chaotically, because the wizard thought that it would be best to run away, having already expended his daily powers in previous battles, while the rogue ran forward towards the enemy. That kind of took the option to retreat off the table, so the wizard wasn't happy. The enemy troops consisted of the enemy general on his horse, two tar devils with ranged attacks, the spitting drake who had run away from the previous battle, and 8 lowly Iron Circle mercenaries.
The tar devils proved to be a nuisance, because they threw burning tar balls that slowed the players down. The spitting drake and the minions died quickly. The enemy general had at first run forward, but except for one area-of-effect attack that dazed several players didn't manage to do much damage. Thus seeing his troops fall around him, he retreated, jumped on his horse, and used his action point to escape. The players mopped up the remaining tar devils and the battle was over. While three combat encounters in series is obviously a combat-heavy part of an adventure, the series adds some strategic elements to combat, as the players need to ration their daily powers and healing surges. In this instance that had worked out rather well, and the players still had had enough reserves for that third battle.
So now the players returned to the main battlefield, where the villager rebels and their elven allies had in the meantime won the battle against the Iron Circle main army. This had been a major victory, as decided by a calculation of victory points based on the adventures of the players. Basically their previous actions, like eliminating the threat of the bullywugs to the village of Tor's Hold, or helping the elves with their problem with the skeletal mage, had added troops and other benefits to the rebel army, allowing it to win. But while the Iron Circle was soundly beaten, their general and his surviving troops were still holed up in the Iron Keep in Harken, where they hold the previous ruler of the barony, Baron Stockmer as prisoner.
Now it is up to the players to see how they can deal with this situation and take Iron Keep. The elves decided that the Iron Circle wasn't much of a threat to them any more, and want to go home. The villagers are enthusiastic, but don't have the training or equipment to storm a castle. The council of war is happy to let the adventurers decide how to approach the situation. This is where the adventure gets more "sandboxy", with anything being possible.
Here the wizard contributed an idea: Not all the Iron Circle mercenaries are dead, some have been wounded or taken prisoner by the rebels. And as mercenaries aren't known for their excessive loyalty, one of them might be persuaded to help the adventures if the pay is right. Thus using his intuition skill the wizard found a mercenary willing for 50 gold in advance and 50 gold afterwards to return to the Iron Keep, and open the gate for them in three days when it is his turn to guard it in the night. After some discussion about the pros and cons of that plan, the players decided to go for it. But the execution of this plan is left for the next session.