I think evil or neutral characters would have a lot more draw for me if there were traitorous or a more even distribution of evil characters to band with.
In FO3 there were the slavers you could join and the slavers in the Mall. There may be a couple others, but mostly the other evil characters were not able to be aligned with (the enclave comes to mind) while any good person would treat you like trash for being aligned with them.
In NV, the only people that seemed evil that you could align with were the powder gangers and the legion. The rest of the population seemed to be wholly against them.
Maybe I just fell short in fully exploring the evil character play through, so if there's something I missed, please let me know.