Well I think we can safely assume that Palpatine was just plain “evil.” Vader was however corrupted by evil (the dark side, etc.) and Kylo seems to do evil in an attempt to do good.
Whereas the OT had a very Tolkien-eque approach towards evil, e.g. somewhat symbolic and straight forward, but still representing real-life fairly well but not to blatanly, TFA just seems to go straight for a more realistic depiction of fascism and ideology gone wrong.

I also found an recent interview with Domhnall Gleeson very interesting where he described Hux’s motivation as (and I’m paraphrasing) a need for control and as with all fascists a fear of “individuality.”
Although I appreciate the OT’s somewhat easy way to approach these subjects; such as imperialism, fascism, etc. I do kind of like how TFA seems to take it one step further, as well as making it more topical and relevant to modern day sensibilities. The OT’s somewhat straight-forward Nazi references have been updated somehat and the new focus has become more political and nuanced. We know seem to get more of a focus on what is going on inside the minds of the bad guys.
A lot of these things were implied in the OT, and somewhat explored in the EU, but TFA really seems to have run away with it.