Green Mars

It took me five years of intermittent attention to finish it, but I finally made it through. This is an incredibly dense book whose glacial pace matches the glacial pace of the plot itself. Slow, plodding, and choked with scientific minutia (both presumably real and clearly imagined), this is the hardest of hard sci-fi. If you're very interested in the prospects of establishing a human presence on Mars, or perhaps in the psychology of extreme life extension, you may well love this book. Just make sure you have time to focus and settle in for long passages about things like planting genetically engineered lychen.