Spock could have been
a really silly character in a lesser actor's hands. But Nimoy turned him into something almost Shakespearean. There are few more complicated, yet accessible characters in all of drama, much less sci-fi.
The character of Spock embraced two parts, two worlds and in the amalgamation created a greater being than if he'd been solely in either one. IDIC is a great philosophy, and it was embodied in Spock.
Nimoy did a few other nice characters on Fringe, and here and there that don't get as much recognition. He was a great actor and by all accounts a good person.