SF Signal had a Mind Meld feature a little while back that asked participants what science fiction or fantasy book they would like to experience reading for the first time again. I don't really have an answer to that. I often get a lot of my enjoyment from a book when I'm not actually reading it- when events or characters or ideas from it are just rolling around in after my head I've finished it, or while its still in progress but not actually in my hands; the experience of actually reading the book, while still very important, is often less central to me than it is to many people. Don't ask me why.
It did, however, get me thinking about which books made the biggest impression on me upon reading them for the first time, which is something I'm better equipped to answer.
The Night Face by Poul Anderson
This is part of Anderson' vast Technic Civilization future history- which I knew nothing of at the time, but it stood fine on its own. Human interstellar civilization is starting to dig itself out of the ashes after a long period of chaos and barbarism, and several human worlds that have made it back to the stars mount a joint expedition to another human world that has been completely isolated for thousands of years.
This wasn't quite the first Poul Anderson book I read, but it was close, and it was the first one to really show me some of the qualities that would make Poul Anderson my favorite science fiction author. Much of Anderson's work is pervaded by a sense of melancholy and an ultimately tragic view of life that exists alongside an energetic sense of discovery, adventure, and heroism, and The Night Face has both.
The part I always remember most is at the very, very end. One sentence, three words, and rereading it still rips my heart out just like the first time.
Side note: The book was originally published under the name Let the Spacemen Beware!, presumably because the publisher thought that the book's dangerously high levels of awesomeness needed to be counterbalanced by giving it the most generic name for a science fiction story ever conceived by man.
The Golden Age by John C. Wright
Science fiction based in post-singularity or "post-scarcity" sorts of settings generally don't do much for me unless it's unusually well-done, but despite this Wright's Golden Age trilogy -The Golden Age, The Phoenix Exultant, and The Golden Transcendence- are among my favorite books.
The first book in the series quickly demonstrates much of the reason for that. From the very beginning the the sheer density of ideas and imagination was stunning, with ideas that could provide the basis for a complete story or even a novel by themselves sometimes appearing on literally every page. And yet I never felt overloaded, overwhelmed, or confused- Wright does a masterful job of it immediately throwing the reader into a radically changed world and making it comprehensible.
Rolling Hot by David Drake
One of Drake's Hammer's slammers military science fiction stories, first published on its own in 1989 and now included in the collection The Tank Lords. This is the big one for me.
I picked up an old copy of Rolling Hot in a used bookstore in my late teens. I knew of Drake, slightly, but I hadn't read any of his work. I was interested in military science fiction and had heard good things about him, so I picked this book put more or less at random. Like Drake's other Hammer stories, it's about a group of mercenaries in the future, heavily influenced by Drake's own military experience. The characters are members of an armored cavalry unit hired to fight on one side of a planet's civil war, plus a a young war correspondent who finds himself dragooned into accompanying them; To the best of my recollection, the cause of the war and the nature and motivations of the two sides fighting it are never mentioned.
It was probably the most emotionally grueling experience I've ever had with a book, or with a work of fiction in any medium. I read it quickly, entranced. I can't really describe what finishing that book was like; it was psychologically numbing and overwhelming at the same time. I felt like someone had driven hooks into my gut and torn my insides out, while part of me felt it happen and part of me just impartially watched it through a window.
The book has some heartbreakingly sad moments, but it wasn't just that. Ironically, much of Rolling Hot's tremendous emotional effect on me was for much the same reason some people have accused Drake of glorifying violence or writing military "porn": The book is written with the understanding that people trapped in awful situations frequently don't have the luxury of consciously feeling the emotions that might be appropriate to the situation if they want to remain at least somewhat functional, and the way it is written thrusts the reader inside that mindset.
If someone doesn't understand what the conspicuously flat affect with which Drake often describes violence and death actually signifies (and/or has some sort of preexisting antipathy towards soldiers or warfare as subject matter or military science fiction as a genre), I suppose it can seem like callousness or indifference. But when I first heard that some people interpreted him that way I was utterly baffled by how anyone could think that, when the sense of pain and horror that suffuses much of Drake's work seemed so immediately palpable and obvious.
I've had other books affect me emotionally, but Rolling Hot was a book that had a more directly personal emotional relevance. Despite being based on a situation far removed from my own life- armored warfare being fairly uncommon in late 20th-century Illinois- Rolling Hot spoke to me in a way that nothing else I had encountered did, though I didn't really understand why at the time. I quickly began buying all the David Drake books I could find, and he's among my all-time favorites today.