I've used it since early on--it is a great little app for quick photo retouching and adjusting. It's fast, also--I've tried Photoshop on the phone and tablet and was never impressed by its speed. (I've used Photoshop for over 20 years now.) I haven't had a chance yet to look really closely to see if the edit quality is as good as Photoshop but it sure seems like it does just as nice of a job.
One of the best image tweaks is the Ambiance control--without getting technical, it does some "magic" by changing the dark and light levels and saturation to put some life into a photo. You would find this under Tools / Tune Image / Ambiance. If Ambiance adds too much color, I will use Saturation to knock it down slightly. I also use Shadows and Highlights to enhance or knock down anything that is out of whack. It helps to keep the phone set to take HDR+ (or even HDR) photos, so Snapseed has a good quality image to work with.
Before:
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After (note the enhanced darker areas, like shadows and the woodgrain cabinets):
The Perspective adjustment is good for straightening a building (to get rid of that "falling over backward" effect, since smartphones can't have tilt/shift lenses
). This is just a quick example I ran through, so it's a bit sloppy.
Before:
After:
In recent weeks they have added more features, including some stylizing options and frames. I tend to skip over those, unless I really want to "grunge up" a photo (like I did with my "too many cars" photo I shared on Instagram):