I read this book when I was 14 - it was one of several that my English teacher recommended, not as part of the school curriculum, but because he thought they were good books (these were halcyon pre-National Curriculum days where teachers could often follow their own enthusiams, and thus build the same in others).
I cannot recall what else he recommded now, but Red Shift simply blew me away then, and continues to have an effect today - 30 years later.
My friend and I read it at the same time and discussed it endlessly. We were gripped by everything - the style, the story, the lack of a traditional narrative thread, the switch between times - and viewpoints, the meaning (if there was one).
Its not a perfect book - the Roman episodes do not work entirely well at times, and returning to it now its a bit dated - but that does not matter when you can be so gripped by the pace and drive of the book (I will not say "story" because that would imply a structure that it does not have - and it is that too that fascinates).
It changed the way I looked on writing, and the way I wrote (indeed maybe still write sometimes). The power of the short sentance, and well chosen words. The way in which the reader fills in the gaps to the extent that every reader probably reads a "different" book.
Red Shift is at its heart a teenage novel (indeed it was probably one the first books aimed at the teenage market, an age group that - and it is hard to believe this now - was incredibly poorly provided for right up to the early 80s), and perhaps its only teenagers who appreciate the structural iconoclasm because many older readers hate it. I'd urge anyone to give it a go - relax and dive in. Let it flow over you. Emerge at the other end (its not a long book), think a bit, then dive in again... and find a whole different story each time.