AFnord: Glad to be of service. Remember that most people are unable to play serious evil campaigns, it just feels wrong, but playing slightly silly evil, like dungeon keeper or Overlord is quite doable for most. The evil campaign that I was a part of a while ago quickly devolved into rather far fetched "masterplans" and arson (as we were trying to build an evil lair, we needed workers, but most evil species make poor craftsmen, so we decided that slavery was the way to go, and who make for better craftsmen than dwarfs? So we started to raid dwarf caravans, in the hope to be able to capture some good dwarven craftsmen)
Fenixp: Actually, evil for the sake of evil is silly and people will act like idiots during it (that's why ditching aligment system entirely is a good idea IMO) However, if you give 'evil' party an interesting goal, they might just start roleplaying properly - of course, finding an interesting goal for evil party is pretty hard.
There might be a third way, giving good guys enough motivation to play evil for a "greater good" or because they're emotionally blackmailed. Putting them in a situation where they have to act in a way that might seem evil from the outside while in truth they have no choice unless they want to risk other bad things happening (to more people or to their loved ones or anything important to them) - but of course they can't tell anyone. Then making them feel like tragic heroes who are treated in a unfair way by their environment, including self-righteous "good" people who always put dangerous obstacles in their way or insult them or use shady tactics in order to catch your "bad" guys. Chances are the players will become angry and vengeful and hate these "good" NPCs with a passion.
The heroes of revenge movies would probably be seen as cruel madmen by large parts of society in the story, especially if the people don't know their reasons for going on a rampage, while from the perspective of the heroes they are only righting the wrong done to them and their loved ones. Your players don't have to feel like the bad guys, if that's not their thing, but you can make them tread more ambiguous grounds, >:D
