You've just asked this question at a very opportune moment – Stephen R. Platt, author of Autumn in the Heavenly Kingdom (2012), has recently written Imperial Twilight: The Opium War and the End of China’s Last Golden Age, which will become available later this month. I've yet to read any serious academic reviews in full, but given the quality of Autumn in the Heavenly Kingdom it's probable that it will be well worth looking into. In the intervening weeks, though, consider Robert Bickers' Scramble for China: Foreign Devils in the Qing Empire, 1832-1914 (2012) or, for a related topic, Frank Dikötter, Lars Laaman and Zho Xun's Narcotic Culture: A History of Drugs in China. Whilst not exclusively on the Second Opium War, Platt's Autumn in the Heavenly Kingdom does contain sections on it within its wider narrative of the civil war between the Qing and Taiping, and is definitely worth checking out.