Vader was the the one. The prophecy said he would bring balance to the force. He did he bought the Jedi numbers down to two. Two Sith Two Jedi sounds pretty balanced to me.
Another note force lighting was not restricted to the darkside. Yoda used it in Ep II to show Dooku that he was not as powerful as he thought.
The powers are the same for both sides of the force. It is just that the Sith like to use the ones know to do harm. Where as the Jedi are diplomats they prefer the simple mind trick.
My understanding (which I've gathered from the RoTS novel) is that the Jedi and the Sith follow the same religion, but different philosophies. Whereas the Jedi detach themselves from all desire, the Sith are greedy and care only about possession and power. The Jedi look outwards for their wisdom, by using compassion, whereas the Sith look inwards.
In the novel Palpatine says "It is said that if one could entirely comprehend a single grain of sand--really, truly understand everything about it--one would, at the same time, entirely comprehend the universe. Who's to say that a Sith, by looking inward, sees less than a Jedi does by looking out?"
The Sith gain unnatural powers by choosing the dark side. They can cheat age and death and can remain acrobatic into old age. As for Force lightning, that is just a Force push pushing electrons together in the air. I guess the Sith also aquire advanced vision which enables them to see eletrons. The Jedi accept death as a part of life; they follow the will of the Force. Sith on the other hand use the Force to fit their will.
The Jedi gain power through understanding, the Sith gain understanding through power.
Try to keep to the movies here, folks! Using Palpatine's cloning trick or calling on Force Storms in the EU is irrelevant...and don't give me crap about it!
DarkAge is entirely right, for the most part.
The Dark Side is the quick and easy way to power, which does not require much learning and tutoring, for the most part, to become powerful. Fueled off of negative emotions (anger, hatred, fear, jealousy, arrogance), it provides the user of the Dark Side great powers relatively fast.
The Light Side is less easy to learn, and requires much learning and tutoring. In the end, they are just as dangerous and powerful as Sith when they are ready.
The Dark Side also provides weird defects, to some degree. Lightning is one such thing, preventing death another.
A sith cannot cheat death IMO. Palpatine only used that to seduce Anakin to the darkside. Immortality cannot be granted through greed, hatred and anger, all the emotions that cause suffering and decay within.
Sure, the darkside will give you some pretty sweet powers, but in the end it will only kill you.