I actually also prefer the KOTOR games to the movies, even if I can only say it's because I spend consistently more time with them than the movies (You can argue games versus movies in that respect though, interactive versus passive entertainment, length, ect ect.)
That said, I find it hard to be evil in the first game. You miss out quickly on a very good character, you make the game harder than it needs to be in a few situations (Using violent means as opposed to diplomatic solutions with more rewards) and it's just morally difficult as a gamer in some cases, such as the choices given on the Wookie planet especially and with your own partners.
The second game makes it much easier to be evil and menacing without having the moral drawbacks, because you won't be wrecking your own characters and pathway at the same time. Similar rewards, pathways, options and abilities, not to mention you get a better character going the evil route and some early bonuses in fighting when you consider Force Shout tree and Force Lightning tree.