I've read in quick succession recently two novels by an up and coming SF writer named John Scalzi. I've been reading his blog and he brought up an entry he made a while back concerning entry level SF. Specifically, SF for people that don't read science fiction.
Personally I have always found good science fiction to be entry level science fiction. Every new science fiction (or fantasy) novel has to introduce readers to a new universe and a good writer should be able to do that for a long time SF reader and someone that has never picked up a SF book before. I think Cormac McCarthy's "The Road," Roth's "The Plot Against America" and Atwood's "The Handmaid's Tale" all straddle that line nicely.