Evil is just a little...predictable, if you know what I mean. People will hate you if they know your nature, and you probably don't care a great deal about the rewards for being evil such as money, as you should be doing evil for evil's sake (though I guess this only applies to Chaotic Evil characters).
Actually, that applies to Lawful Evil characters. A lawful evil person does evil because the "laws" of evil dictate it, or a specific god they worship commands it. A chaotic evil person is more about being evil because it's funny or because it pays.
But I agree, being evil can get pretty predictable. Like in Fallout 3, while some of the evil choices were really quite funny, what other choices were there? For example, the Oasis quest had a lot of different paths you could take. You could kill Harold because his existence was painful, let his seeds spread throughout the wasteland so it would become green again, make it so his seeds will never spread any farther to promote the Treeminder "cult", or just light him on fire with a Flamer. Out of all of those options, I can only see one as being truly evil: lighting him on fire (which is hilarious, by the way). The only other one I'm iffy about is stunting his growth, but that's more of a gray area than anything. What I'm trying to get at is that you'll be doing some type of good for all of those choices except burning him, and that usually applies to most situations. There's usually only one "evil" option for most things, and they're usually an obvious choice. If I was evil and saw a tree man, the first thing I would think of is "burn him". The same applies to the Megaton quest. If I was evil and saw a town built around a nuclear bomb, the first thing I would think is "set it off".