The last two books I finished, Conversation in the Cathedral by Mario Vargas Llosa and Babel-17/Empire Star by Samuel R. Delany, have been reviewed and analyzed to death, so instead I'm going to give my initial, visceral reactions to both. Know that I find both novels to be wondrous works in their own right.
I found Empire Star - the novella that accompanies the main novel - to be just as interesting, but in far different ways. Empire Star is half Flowers for Algernon and half mini-bildungsroman. Though Babel-17 is not, Empire Star is cyclical in process and it's always entertaining to watch a writer working toward something you know will pay off (in dividends!!) in a later work.
Empire Star is also a meditation on the actions of our choices and our perception of - not necessarily what is right and wrong - but how we choose what is right and wrong. Delany uses three different perceptions of thought - simplex, complex, and multiplex - to make his argument. (This might be a simplex way of putting it, by the way.)