When done right, sci-fi movie villain deaths can be incredibly satisfying. You know when villains have done their job right when the audience hates them with a fiery passion. The director has done their job if they allow the audience to blow off all that steam by watching the villain croak in the most gruesome (or at least karmically satisfying) way possible. Bonus points if the method said villain used to maim or torment people is turned around and used against them.
The world of sci-fi produces some of the biggest and baddest villains around, and the bigger they are, the harder they fall. When the villains from this genre are given a taste of their own medicine, it involves, say, fiery falls from skyscrapers experienced in slow motion due to all the futuristic drugs they're on. Or, if a bad guy is really unlucky, using a kaiju to terrorize thousands of people results in an opposing kaiju showing up to throw him hundreds of feet through the air to his demise. Basically, it's a genre filled with brutal villains who face incredibly brutal deaths. Vote up the villains that got exactly what they deserved.