A non-fiction account, but one that reads as well as a novel, is Capt. Cavalie Mercer's
Journal of the Waterloo Campaign. It's his actual journal, done in a fairly terse style.
Another great eyewitness account, albeit from the Peninsular Campaign, is
Recollections of Rifleman Harris. Harris was a common foot soldier and so presents a very different account of life in the British Army during the Napoleonic wars than that of Mercer.