Eye in the Sky by Philip K Dick
Occasionally I wonder why I persist with Philip K Dick, then I read something of the standard of Eye in the Sky and I remember. Like many authors his quality's not consistent, but when it's good it leaves you feeling like you've experienced something, not just read the words on the pages. First published in 1957, Eye in the Sky does have some dated elements (the whole fear of Communism strand seems bizarre) but if you accept that it's clearly from 50s America it's an original and gripping novel that's worth a read.
Electronic engineer Jack Hamilton and his wife Marsha are caught up in an accident at a new particle accelerator, together with a friend of theirs and five strangers including the tour guide who was showing them round (physics tourism!). When Jack wakes up in hospital something doesn't feel right and he soon realises that the world no longer obeys the physical laws he's used to, seemingly ruled by a capricious Old Testament style deity. He struggles to adjust to an incomprehensible world where all his skills and knowledge are of no use, but that's just the beginning and together with the other seven victims Jack works his way through a series of trials and difficult situations.
One of my frequent PKD complaints is the hastily-sketched characters, passed over quickly so that the plot can happen. With Eye in the Sky the characters seem more substantial, and an interesting mix - though the boy who later is mentioned as about 11 comes across as much older throughout. The situations lead to shifting loyalties, suspicion and temporary alliances, and bring out different facets of the various characters. The pacing is good - it picks up speed as it progresses, and there are ambiguities and hints along the way.
Strictly speaking it's probably more fantasy than science fiction (and even veers towards horror in places) but that hardly matters - it's an entertaining read, and more importantly it makes you think (the mark of good sci-fi? Discuss...). If you've ever enjoyed anything by Philip K Dick I'd recommend this, and if you haven't, you could do much worse than start here.