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.
Snapseed makes it easier to add drama to your photosReal photo editing apps have curves.
Snapseed doesn't see quite the amount of updates that other Google-owned products do, but each one lately has been pretty significant. The name of the game for the latest is the addition of curves. Essentially, what this new feature does is allow manipulating things like contrast, brightness and color intensity in a given image. Oftentimes, it's one of the easiest and most dramatic ways you can edit a photo.