In our campaign, we run evil characters. It's a refreshing change for the guys, who are pretty terrible heros in other campaigns to tell the truth. Now we don't have to treat, "Well, we could just kill everyone." as a joke. It's also a challenge to me, figuring out how to keep them immersed in the story. Why should they put their necks out for this guy or that guy? It's not so easy when you don't have "Well, it's the right thing to do." to fall back on. Creating a delicate balance of bad guy and antihero in our sessions has been a blast.
Last year for my birthday, one of the guys gave me the King of the Trollhaunt Warrens for a gift. I thought I'd pull it out and add it to our adventure board. Sure enough, they chose it, and off we went. I don't like to railroad them into story, so I gave them a package to deliver to the area, sort of perused through the books and we very loosely started up the adventure. Their involvement, as always, is up to them. When they intercepted the letter letting them know that Moonstair was getting help from eladrin reinforcements, one of my players threw me a bit of a curveball. He didn't care about the troll assault, really. Yes, he wanted that enchanted sword, but first, he really wanted to stop the eladrin from coming to help. He wants to defeat the eladrin reinforcements, and then deal with the trolls at his leisure, Moonstair be damned.
So, I put away the adventure module completely, and tried to think of something that would really make this little detour great for the guys. They've fought groups of enemies and have been significantly outnumbered before, and they always thrive. Strategy comes heavy into play with them, and they always surprise me with their brilliance, putting away encounters that I thought would be tough by virtue of how they play off each other.
So I decided to give them something more in that regard this next session. A full scale battle, soliders and generals, a small army against my sweet little group. I almost hope that they die horrifically, because it would serve those evil bastards right.