As a Cambridge NatSci graduate I loved the visceral detail of the decaying 1998 setting, though Benford failed to predict one element of real life decay, the extinction of independent bookshops - he still has Bowes and Bowes open and staffed by attractive young women, when in real life I think it closed in the early 90s.
But it's a bit less satisfactory as a novel than I remembered it from my first reading. Both ends of the time line feature almost entirely male working environments, with the odd distant woman scientist collaborating but the protagonists enduring varyingly problematic sex lives with their various female partners. I was not completely convinced, though I can see that it's written from the heart.
And the sending-messages-through-time plot, the core of the book, actually doesn't work very well. Rather than the messages from 1998 inspiring scientific research to get the world out of the mess it is in, they accidentally prevent the assassination of John F. Kennedy, and that seems to be the crucial point of departure which kicks the 1963 world out of our timeline and into a better one. Why Kennedy's survival should make the difference is not really explained. (And the elaborate system developed by the 1998 scientists to check that their message is getting through is unnecessary given that their telephone system still works.)
Though I do like the nod to Silverberg's Dying Inside, whose protagonist makes a brief appearance on page 273.
Timescape won the Nebula in 1980; of the other nominees, I have definitely read the Hugo-winning The Snow Queen and The Shadow of the Torturer and I may have read Beyond the Blue Event Horizon but am not sure. I have not read, or even heard of, Walter Tevis' Mockingbird or Robert Stallman's The Orphan. I think it's one of those years when the Nebula went to the kind of novel that would normally have a better chance of winning the Hugo, and vice versa.