One problem I have sometimes found while running, briefly observing, or playing in evil campaigns (and good ones, coincidentally) is the strong tendency toward neutrality, in some PCs.
A lot of the time, in other words, I feel that players would be more honest if they wrote 'N' in the alignment area of the character sheet, regardless of whether the campaign has been designated as evil, good, lawful, chaotic, or some combination of these.
I'm not sure whether that would be because most people are closest to 'N' or whether it's the easiest alignment to play, or some other reason.
Anyway, hopefully you will find that this trend does not apply to your group(s). And if it doesn't, then I'd say you're in for some fun and interesting roleplaying experiences.
Currently, the evil D&D campaign I'm running is going better than I had expected. Recently, after unintentionally liberating a city from another evil group's psionic and martial shackles (!) the character party let off steam with some nice calming torture and corruption. Since then, they've formed an unsteady alliance with a different evil group (this time with similar goals, it seems) who are publicly under a banner of goodness and all that. Now sacrifices and the planes have started to make their presence felt. I'm finding that it's the most fun campaign to run, at present.
IMHO, I think what an evil campaign requires is that each player throw him- or herself wholly into the character, while distancing from that player's own personality, priorities, beliefs etc. More than is usually the case in roleplaying, I mean.
Chimera said:
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About 10 years ago another group I played with took a stab at an evil campaign. One guy got a bit too into it and started actually describing his torture of peasants, which was a bit more than the rest of us were comfortable with. Saying you're torturing them = ok. Describing it in detail = NOT ok. A short while later he quit the game, saying we weren't letting him have any fun. Quite a mind twister considering the guy was an evangelical christian.
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Par for the course, no?
...couldn't resist.