Evil is lame for two reasons. First, because it's too easy to be good. Take the water beggar outside Megaton for an example. In the 'real world' giving him pure water would be a good act not just because you helped him, but because you gave up pure water to do so. Self-sacrifice and all that. It's broken because the Wanderer doesn't need to drink, no matter how much running across the Wastes in the middle of the day he does. And even if you do give away all your pure water and force yourself to drink dirty water, Rad-Away is so common and you can carry an infinite amount/go see the doctor who has infinite Rad-Away in exchange for a few measley caps, radiation isn't a threat at all. Second, following from that, since being good is so easy, you have to want to be evil/be doing evil for kicks. Like blowing up Megaton being the first non-story quest you can get. The worst you can be in the Vault is a snarky jackass (even killing the Overseer is treated as misguided heroism), but you stroll out and decide to murder a whole town because...? Since you have to be trying to be evil, Fallout 3's 'Evil' is just psychopathy, not self-interest.