About the best thing you can say for World Atlas is that it gets right to the point. The map app lets you view four different styles of world maps, with little to no fuss. Unfortunately, it only lets you view the maps, a function that Google Earth and the default iPhone Google Maps app already perform quite well.
To be fair, it's perhaps slightly easier to see different parts of the world in the World Atlas app than it is on your standard Google map. Once you choose the style of map you want, from political, physical, time zone or satellite, you can pick the continent you want to browse. This doesn't mean you can't scroll the view over to another continent, though, so if you pick South America, but get a hankering for Asia, you won't have to backtrack.
You can also zoom in on the maps, which is probably most effective when looking at the physical or satellite maps, and less so for the time zone map. Still, sometimes it's the little things that count.
Strangely, for an app called World Atlas, the most interesting part might be the collection of national flags available for viewing. It's a bit of a let down that you can't see bigger images of the flags, or even some facts about the countries, but at least they provide something different to look at other than maps you could have seen in many other places.
With so many options available, both free and otherwise, World Atlas doesn't have a lot going for it. That's not to say it's a terrible app. It is, as advertised, a world atlas app. It just isn't much more, and that's the real problem.