There are presets available (similar to Adobe's Lightroom Mobile's, even though it doesn't offer curves proper), and, if you want, you can fine tune individual color and tone channels as well. As the latest Snapseed entry on Google+ notes, the face detection has gotten a "try harder" option as well if the app doesn't get it quite right the first time. The update is out now for both Android and iOS and you can grab it from the links below.