I like young adult novels because they tend to be short. There's been a discussion recently amongst independent game developers about how long people expect games to be relative to their price. One of the mistaken points I've seen made a few times is that it's only games consumers that judge their media by its length. I'm pretty sure there's a pressure in the adult fantasy/sci-fi genre for novels to be bloated, poorly edited messes. A book needs a map in the front, “Part One of the Demon Kingdoms Saga” on the back cover, and seven or eight hundred pages of typo-laden prose in between. Fortunately you can go to the young adult field and find tightly-plotted, well-characterized books that won't waste your time. Here are two:
Ship Breaker by Paolo Bacigalupi. An oil-less near future on the flooded Mississippi coast. Nailer, a child laborer (the eponymous ship breaker) falls in with a shipwrecked princess on the run. The characters are vividly drawn, the drama is intense, and the plot comes together well. Nailer's abusive father is a particularly strong villain. Not a cheery book but the atmosphere is thick and novel. Impossible to put down once started. Bacigalupi has also written a (much longer) adult novel in similar vein, The Windup Girl.
Leviathan by Scott Westerfeld. Westerfeld, already a prolific and accomplished YA writer, tries his hand at this newfangled steampunk thing. It works out pretty well, and has a sequel coming out in a couple of months. It's an alternate history version of World War I where the British have got genetic engineering down pat (with which they create the requisite steampunk dirigibles) and the Germans have gigantic walking fighting machines (because really, what universe should not have these?) Deryn, a young girl, hides her sex to enlist on a dirigible, shipwrecks and falls in with a prince on the run. Similarly un-put-downable.