Yes, the Sith really are evil. Yes, the Jedi really are good.
The entirety of the Sith philosophy revolves around selfishness, while the entirety of the Jedi philosophy revolves around selflessness.
A true Sith wants to become the most powerful entity in the universe and subdue absolutely everything to its own will. A true Jedi simply wants to do what is right.
The problem arises when we see the Jedi defending a decadent capitalist Republic ruled by rich corrupt elite. The Sith Empire provides a stark contrast to this as even slaves have the potential to work themselves to the very top (as is the case of the Inquisitor).
So yes, the Sith philosophy is evil. It embraces the dark side and encourages violence and murder. And the Jedi philosophy is good. It embraces the light side and encourages peace and kindness. But are the Jedi and Sith like this in practice? Usually, yes. But not always. And it's that not always that is the problem. The Jedi should not be supporting a Republic that actively encourages a huge rich-poor gap. The Sith, on the other hand, have the perfect system for their philosophy. It rewards merit rather than wealth. But their philosophy itself is the weakness. When everyone is out for themselves, the no one is helping each other. This is why the Sith always ultimately fail. They end up killing each other off and cause their great empires to fall.
A Jedi Empire would pretty much be the perfect system if Jedi were allowed to marry. I would be rather unbeatable, people would be promoted on merit, and because of the Jedi way, there wouldn't be any poverty. No one would be homeless. No one would be starving. And with a galaxy's worth of resources, you can't tell me that this couldn't be done. But, because the Jedi always shy away from power, this would never happen. And that is one of the Jedi's greatest faults, that they look at a position of authority as a position of power rather than a position of responsibility, a responsibility that would be best left to people like them rather than corrupt politicians or evil Sith. A true Jedi without selfish desires and only benevolent thoughts would make a perfect Emperor.
To be perfectly honest, as the Jedi Knight in the game, if I ever had the opportunity to become Emperor of the Sith Empire, I would take it without hesitation. Taking it would mean galactic peace in our time, and the authority of Emperor would allow me to make the galaxy a far better place. Of course, the immediate result would almost certainly be civil war.