I usually do several playthroughs of games with moral choices, each time taking a different approach. I find it interesting and a lot more fun to see how the consequences and reactions are different depending on my level of douche-baggery.
My first 3 playthroughs usually go something like this:
1st. I act the way I believe I would act if it was myself in the situations (as best as I can, I can't say for sure how I'd react on some situations because a lot of them are pretty ridiculous). Usually this playthrough is mainly good, maybe with a bit of law breaking and necessary killing, but only a bit. And making sure there is something in it for me when I'm risking my neck.
2nd. The super good playthrough, where I help and protect everyone I can, not being concerned about the reward. No killing of innocents or enemies if possible (some games obviously it can't be helped.)
3rd. Evil. Evil, evil, evil, EVIL. This is usually a complete mess around, when I'm just Chaotic Stupid Evil and I'm just horrible, murder, steal, pillage, burn and insult everyone I can.
Most people I know tend to do something very similar. I think the evil mass-murdery style just allows us to act in a way (hopefully) we would never be able to act in real life. Which is surely the point of gaming in some respects, to be able to do things we can't do ourselves, for a bit of fun.
(Yay! My first ever post here... I'm going to bask in it).