I will geek out for a moment. People say that Tolkien created a conflict that was purely black and white with no real psychology behind the bad guys. But he does lay out the differences between Sauron and Morgoth in an essay in Morgoth's Ring that is quite interesting and could be relevant to the tv series.
"..when Melkor was confronted by the existence of other inhabitants of Arda... he was enraged by the mere fact of their existence... Morgoth would no doubt, if he had been victorious, have ultimately destroyed even his own creatures... Melkor’s final impotence and despair lay in this: that whereas the Valar could still love Arda Marred... (in contrast) Melkor could do nothing with Arda... even left alone he could only have gone raging on till all was levelled again into a formless chaos."
"Sauron had never reached this stage of nihilistic madness. He did not object to the existence of the world, so long as he could do what he liked with it... he loved order and coordination, and disliked all confusion and wasteful friction. Sauron had, in fact, been very like Saruman, and so still understood him quickly and could guess what he would be likely to think and do... (Sauron's) plans, the idea coming from his own isolated mind, became the sole object of his will, and an end, the End, in itself."
"Morgoth had no plan; unless destruction and reduction to nil can be called a plan. But this is, of course, a simplification of the situation. Sauron had not served Morgoth, even in his last stages, without becoming infected by his lust for destruction, and his hatred for God... He probably deluded himself with the notion that the Valar (including Melkor) having failed, Eru had simply abandoned Eä"
Sauron was originally a maiar that served Aule, who was kind of like a greek god of smithing. Hence is love for order, coordination, and perfection. He saw Morgoth as someone who could more quickly realize his plans & designs because he was the most powerful (and charismatic) Valar. But as Tolkien puts it this decision put him on a path that spiraled downward.. to the point that implementing his plans and controlling others became the end it itself. Sauron was a master smith so he created the rings to do exactly that.
Morgoth on the other hand was closer to pure evil. He wanted to destroy the world simply because he was not its sole author/god/king.
