Well, I have lost my copy of 'Farthing' that I was reading, the 2006 Nebula nominee by Jo Walton. It'll come back eventually, but while I wait for it I've decided to read 'When Harlie was One' by David Gerrold. This novel was nominated for both the Hugo and Nebula award for best novel in 1973-74. Gerrold should be a huge name in science fiction, but he's largely been tossed aside by history. No one really talks about it but Gerrold was instrumental in creating the Star Trek as we know it. Any differences between the original Star Trek series and Star Trek TNG can be directly attributed to Gerrold's influence. He was responsible for adding the executive officer (Commander Riker) and for putting Worf in the show at all. Though he's not even attributed after the first season because of an argument with the writer's guild, they wanted him to have a creator credit which he refused, wanting Star Trek to remain Gene Roddenberry's baby forever. Gerrold also wrote the Star Trek handbook and several Star Trek novelizations. Most importantly perhaps he wrote the original episode 'The Trouble with Tribbles,' which would probably be enough to put him down in the sci-fi hall of fame forever.
In genre circles now Gerrold is perhaps best known for his War Against the Chtorr series, a sort of middle of the road science fiction series that pits the men of earth against an invading group of monsters, I haven't read much of it but know that none of the novels involved have been nominated for any awards. Also the Star Wolf series, which I have read, which is basically Gerrold's take on Star Trek, enough names are changed that he won't get in any trouble but it's an interesting take on what Star Trek might have been if Gerrold had more of a free reign in deciding it's direction, and also if one wants a sex scene involving the Klingon stand-ins and a human being. None of the novels in this series were nominated for an award either, but they're pretty light and fast reads if someone wants an alternate take on the ST universe.
Gerrold was a pretty busy writer, and still is, the last few books of the Chtorr series are still forthcoming, but he has only been nominated for two best novel awards in his career. One for HARLIE and another for 'The Man who Folded Himself.' It's this second novel that wins Gerrold his lifetime pass in my book. There are certain circles of science fiction fans, my circle, which is basically just me, that consider this one of the definitive novels about time travel. It's one of the first novels to end in a recursive loop, and it certainly has the first (if not only) instance of a person having a homosexual relationship with themself. Time travel novels can go in certain directions, the author can allow a paradox to take place or not, they can allow for parallel timelines or not, but in all instances it needs to lead to almost an entropic level of complexity. There are a few time travel novels I don't really like and they're all the ones that act like the sub-genre can be approached lightly and not very much thought put into the mechanics of time travel. I would encourage most would be writers to approach it with care, and if you do feel like taking a light approach use Heinlein's 'The Door into Summer' as a guideline on how to make it work.
When talking about time travel I think there is really one big question the writer needs to ask themself: 'Can the past be altered?' If the answer is yes then you need to wonder if the existing timeline is then destroyed ala 'Back to the Future' or if you then create an alternate timeline like Kang in the marvel universe or Gerrold's character in Folded. If you opt not to create a universe in which the past can be changed you're creating a world like the sort that Futurama had in 'Roswell that ends well', where you can be your own grandfather but it was always that way, or Connie Willis' Oxford series where no matter how you try to alter the past something will always occur to stop you, because the past has already occurred. There are a lot more ways in which to parse the fiction that deals with time travel, but there are great examples no matter how you choose to deal with the mechanics, and I think 'The Man who Folded Himself' is one of the first and the best, no matter how pedestrian the rest of his novels may be, (and I've barely even started HARLIE yet) that one novel totally earns him a pass.
There are a lot of people on the internet reading all the winners for either the Hugo or Nebula award for best novel, and that book is one of the prime examples for why you shouldn't do that. Reading only the winners would lead you to 'Rendezvous with Rama' by Arthur C. Clarke as the winner for both Hugo and Nebula for 1974 when really at least one of them should have gone to Gerrold. I gush more over this book in my review and really I just meant to talk about time travel in general and HARLIE, I really shouldn't get myself started on 'The Man who Folded Himself.'