There are a bunch of reviews on the web so all you have to do is Google Snapseed. I enjoyed watching a few of the tutorials on Youtube and various places around. The UI looks extremely intuitive and very useful rather than some of the other apps out there which to me, look cluttered with useless bells and whistles.

One of the best features (IMO) in Snapseed is the selective editing. You can select a point, then choose the size of the area around it and edit only that area. great for those times when you didn't have an filter on your camera and the foreground was dark but the sky was bright. (What an ND filter is used for)

There are also a bunch of creative filters as well as basic adjustment tools. And knowing Nik Software, they'll likely update the app with even more filters and features in the future. Nik makes great professional software, I'd expect this app to follow suit.

Check out this video as an small example of what Snapseed can do: Snapseed From Nik Brings Infinitely Variable Filters To iPad Photo Editing | Popular Photography

And some other links:

Snapseed from Nik Software