I've been working my way, trainspotter style, through the 1855 for a decade or so now. Fortunately, I managed to tick off the first growths before the prices became stupid.
Yes, I know that much of the classification is very likely smoke and mirrors, as, with one or two very minor exceptions, it hasn't been revised in the 160-odd years since it was drafted. Nevertheless, I find it satisfying.
Here's the wikipedia entry on the classification: