I have gone back and spent some time playing Fallout 3 and Fallout: New Vegas as of late to keep from going insane while waiting for Fallout 4 (although I probably am already). While I think New Vegas is a better game overall (particularly the DLC), Fallout 3 totally kicks its butt when it comes to cool things you can do on a bad karma playthrough.

(Spoiler Alerts?)

Blowing up Megaton is something really really awesome you could do right at the start of FO3. Its epicness went down in gaming history, and you got a fancy house to boot. Being a big meanie also got you access to a few quests in Paradise Falls, a small chunk of content those lame-o goodie goodies coudn't do. Heck, you could team up with slavers in Fallout 2, they gave you a nifty tattoo and some nice caps for peddling those tribals. If you were lucky enough to be playing the U.S. version of the game, you could do "something" to those wicked little "somethings" who kept stealing your stuff. However, If you sided with Ceaser's Legion in NV, you never really got to do anything cool. Being able to consign Arcade Gannon to a life of slavery and a sore sphincter was kind of fun, but not blow up a whole city fun. You could blow up the Brotherhood of Steel bunker, but there was no benefit from it. Watching Cass get vaporized by the Van Graffs was pretty much the only thing that brought a smile to my face, but I could just vaporize her whenever I wanted to. New Vegas didn't even have bad karma exclusive companions like Fallout 3 did, just some narrow-minded comanidiots you would need to kill for not understanding your (correct) point of view.

(I shouldn't have put a spoiler alert, it would have been more evil!)

So let's toast a glass of Roentgen rum, gorge on human flesh, and raise the horns for EVIL! Who else is looking foreward to playing Fallout 4 as a certified scourge of humanity? I am very excited at the twisted possiblities the team at Bethesda has likely cooked up for us.

i know the DLC from NV are good, but i really love alot more the DLC from Fallout 3, Pointlookout and The Pitt, both allow me to see other part of the Wasteland

As for an evil playthrough: I always find the content either extremely sparse or poorly executed when playing as an evil character. I don't even understand the concept between good and evil in video games, as the lines are drawn in different places depending on the person or culture.

Country A goes to war with country B because their beliefs are different and thus "wrong" or "evil", while country B thinks likewise about country A

I'm just hoping the writing is far better in Fallout 4 than in Fallout 3. The whole good vs evil thing was a massive turn off for me, where as I much preferred New Vegas where they explored the politics and beliefs of the factions. People may consider the Legion as "evil", and I would agree their methods are dark, but I when you explore their culture and reasoning they aren't the pure black that one might first color them.

In any case, my characters are usually a dark-grey good, neutral or a survivor plain and simple. When I wiped out the Enclave in Fallout 2 and 3, I didn't consider my actions as purely good or bad. My character did what they felt was necessary for the greater number of people and to protect innocent people, but in doing so they wiped out an entire faction and killed hundreds.

Don't even get me started on Megaton or the main quest in Fallout 3 though.

I like playing evil characters in Fallout. We always play the good guy in other things. Nice to have the option

For the most part I greatly disagree with evil actions such as murdering the innocent and cannibalism and I don't make evil decisions either because they're super jacked up, but I always have a low Karma because I steal and pickpocket so much haha. Speaking of which, it's incredibly stupid that I can lose Karma for stealing from evil factions such as Powder Gangers or the Legion, yet I don't lose Karma and sometimes even get positive Karma when I kill them! WTF? Screw logic, right?