Well if we're going to go flying off at a wild tangent, the most impressive novel I ever read was Asimov's 'The postitronic man.' It remains the only book (apart from HHGTTG) that I've read twice. It had a very hit and miss movie adaptation. The first half was pretty close to the book but then the second half just went very wrong. Where it did succeed was by making the end poignant and giving emotional resonance to the finale. The book brought a lump to my throat both times, just a brilliant ending.