I've started over as a female character, abandoning Alec to the path he's chosen. As a level 20 badass with 2,000+ of every ammo, fully repaired weapons of every genre, and Tesla armor out the wazoo, he was no longer a lonely Wasteland wanderer in need of guidance. He's a Wasteland prince, worshiped as such and patiently awaiting the DLC which will allow him further advancement beyond his current perfection.
In the meantime, Sierra. Unlike Alec, who is saintly to a fault, Sierra is mostly indifferent to the world she's been thrust into. Her service is for sale to the highest bidder—if that happens to be the man who wants to blow up an entire city, so be it. If the highest bid comes from the bloodthirsty ghouls living in the metro tunnels, okay. We're all pals in caps-land. Even you, zombie-faced killah.
There's definitely a different feel to playing as an "evil" character versus a "good" one.
I think, deep down, all of my characters are just neutral. Any time someone ran up to Alec and gave him a random gift for "everything you do for us," I felt inappropriately inflated. I wanted to say, "Hey, I also just killed a random passerby. But thanks." Sierra is being hunted by a group of regulators, but she's hardly a "scourge on humanity." Just because she sold a few citizens into slavery, she's suddenly this massive villain who needs to be detained. Not only do they leave behind utterly worthless corpses (um, those Regulator Dusters? Not even half as useful as the Talon Merc's Combat Armor), but she loses karma for killing them. Even when they start the fight. Unprovoked. And she has no choice but to kill, be killed, or cripple their legs and run like a fat kid caught swiping Ding Dongs at 7-Eleven.
One of the biggest changes, and most eerily rewarding, was blowing up Megaton. Alec lived, loved, and died in Megaton. He could barely pickpocket crucial-info-withholding Moriarty without crying acrid tears of guilt. Sierra, on the other hand, waltzed into Megaton, took "Sheriff" Simms' bobblehead, borrowed Moira's armored Vault suit, charmed Mr. Burke, and blew the place to hell without even introducing herself to the rest of its citizenry scum.
The explosion was brilliant in the pre-dawn hours, and the leftover crater and impenetrable haze of debris clouds is like a waking dream. I love wandering through the Megaton outskirts, kicking Deputy Weld in his not-quite-melted face. Moira seems happier as a ghoul. Gob is no longer slave to the drunken whims of smoothskins. And Sierra has a lovely walking trail on overly-sunny days, so long as her advanced radiation suit is handily nearby.
My Wasteland Lady is more than happy to assist those in need, but doing the bidding of the capitally degenerate is much more rewarding. Literally, with caps and goodies. Sierra had 83 caps to her name before blowing up Megaton and getting into the slaving business. Now she's a multi-thousandaire, buying shotguns and Stimpaks on willy-nilly whims. The emotional rewards which balance out the inevitable Jet addiction and spiraling flood of guilt arrive in the form of "I'm getting a vastly different gaming experience, but I only paid for one game! Someone is getting gypped, but it's certainly not me!" (Outside of Fallout 3, the world speaks in exclamations.)
That doesn't mean the path she walks is entirely paved with gold and buy-one-get-one coupons. Potential best friends flee upon meeting her; all of the sweet and kindly residents of post-apocalyptia find her less than charming. That might have to do with her having a Charisma of 3—she needed those points for Strength and Intelligence, the brainy bully—but nevertheless. It's already a lonely world, made that much lonelier when your closest pals are slavers, who just happen to be paying you to entrap their previous best buds. Her blazon fortune and roomy suite cannot quell the emptiness in her heart; the pain of going home to the mocking bobbleheads who are so tight-knit and yet exclusive in their cerebral Elephantitis.
Of course, she hasn't found Dad yet, the one person who loves her no matter what path she's chosen to plod down. But his approval will offer little protection. I'm sure those Wasteland jerks will just sneer out, "If he's so smart, how come he's dead?" as she kicks their faces in, Radroach-style, and continues her trek through not-quite-damned-for-eternity Karmaville.