This comes up a lot when people are talking about games. Players, at least some players, want to be the villains. They want to be the guys robbing the bank, not the guys stopping the bank from getting robbed. They want to be the ones threatening the world, not defending it. They want to be the ones throwing kittens into trees rather than climbing up and helping them back down. The thing is, there are problems with a game making the players a villain. These problems are amplified for a table top RPG. Today, I'd like to talk about some of these problems.
Villains Seldom Change
The issues that confront a villain as a main character are primarily narrative in function. This shouldn't be a surprise, after all being a villain is a narrative choice not a mechanical one. The first of these problems is that villains very rarely change. See, in most stories the villain takes the role of the antagonist. They, as the antagonist, force the protagonist - often the main character - to go through some sort of change. This change is the emotional/personal arc for the hero of the story. Now, change isn't necessary for a main character, but it helps and stories where the main character doesn't change often leave the audience feeling like something is missing.
In a table top game this lack of change can be horrible because RPGs are nothing if not character focused and a character that doesn't grow will become stagnant very quickly. Think about it this way: conflict forces a person to change. Conflict is also entertaining. If nothing is changing the character, or even testing who they are, then there is no conflict. That's pretty boring.
Villains Are Proactive Not Reactive
This is the big thing that a lot of people don't think about, especially when it comes to table top games. Villains are the pro-active parts of a story. The hero doesn't show up to stop a bank robbery before it is in progress, nor does she raise an army to fend off the forces of darkness when there is no sign that the forces of darkness are anywhere in the area or even considering coming over. No, villains are the ones who set things into motion.
Why is this a problem? Well, for one thing it means that either the beginning of the adventure or plan has to have no player choice involved in it, or that the players need to do a lot of the set up and then give the GM time to figure out what obstacles will be in their way. This may not sound like a huge deal, but compare to most table top adventures where the GM knows who the villain will be - the PCs being heroes naturally they go after villains, right? - lets the GM set things up specifically for that villain and what the players will have to overcome. This setup can take time - preparation - so what do you do when you don't find out until the beginning of the session that the players are going to rob Casino A instead of billionaire birthday party B.
The other solution is to assign tasks to the PCs, but that would imply that they have a boss and no one really wants to be a henchman when they say they want to be a villain. Just like players don't want to be the B-squad to the real heroes in every other game. Why settle for anything less than being the main event?
Legwork is Boring
Considering I'm currently running a Shadowrun game and a lot of Shadowrun is doing legwork this may seem strange, but keep in mind that legwork can be boring. There is a reason why legwork gets montaged over in movies while the fights get slow-mo frame by frame references for what is going on. Fighting is fun, planning is boring. It is also a real tension breaker when you know going into things that you have trump card A, B, or C at the ready, so you don't even get the excitement of "when did they set that up..." that you can with TV shows like Leverage or movies like Ocean's 11.
Now, there are ways to make this more fun, but it is still going to be a big part of the game. And keep in mind, a successful villain score won't involve fun combat and considering villains are pro-active, if things look harder than they should be nothing stops the villain from just walking away. Done right, a villain game would be boring as all get out.
Villains Are Meant To Lose
Not always the case, I know, but the fact is in most stories the villain is meant to lose. This comes as part of their role as antagonist, and also as part of the function in stories they serve. A story where the villain never failed would be boring. A story where the villains never failed would also end very quickly. See, heroes can always be challenged, but eventually what happens with villains? They become rich and retire? They take over the world? These are possible things to happen, but it does get stagnant and stories are written for the villain to lose most of the time. Stories where the villains win? Generally speaking the villain isn't really the villain in that story, even if they're not necessarily a "good guy."
All of this is not to say that the villain game can't be done, but these problems need to be addressed. Remember, the fun thing about rules in creative works is that once you know the rules it is ok to break them because you do them while knowing what the rule should be and why. By all means, do a villain game if you can. Just go in expecting a lot of work from both yourself and the players.