Since I reviewed Nightwatch...

Night Watch is Terry Pratchett's non-parody of Les Miserables, and one of my favorite books ever. Where Les Miserables covers decades, at epic length, Pratchett leans on his long series of novels to provide enough backstory for this novel. The main character, Sam Vimes, started out as a Chandler-esque (read: alcoholic) antihero in "Guards! Guards!", which is a masterpiece of comic fantasy that you should go read immediately.

...And now that you're back, he's almost reached the rank of 'father' when a manhunt for a psychopath and an ill-timed lightning strike send him back into the past. The Bad Old Days. When the city was ruled by an unenlightened despot, and on the edge of revolution. And when Vimes was a raw recruit. Our Hero has to catch the bad guy, keep his younger self on the right track, and above all Not Change History if he ever wants to go home again. And of course he does. In all, it's a very neat adaptation, with interesting points re: nostalgia, revolution, the accuracy of History, and the urge to slap your younger self upside the head.

I rarely recommend Night Watch because it's not a self-contained epic - it builds on the trilogy of Watch books (Guards! Guards!, Men At Arms, Feet of Clay), and two more Vimes-centric books (Jingo; Fifth Elephant; Night Watch). Since they're all excellent - and hilarious - I just recommend Guards! Guards! and assume people will go on from there.