The best Sci-Fi is timeless, like any good novel. That doesn't assume 'new' themes as I mentioned earlier. For me, the better ones create alternate universes or scenarios and use them to examine political, moral, ethical questions and the human condition. A recent read for me was
"The Dispossessed: An Ambiguous Utopia" by Ursula K. Le Guin which contrasts earth "Terra" with another world in which there are no possessions and no laws, contrasting the advantages of each. When you seek free literature, you usually (but not always) get what you paid for.
