Most downloaded apps have those minuscule squares with rounded edges in common, what we called as App Icons.
Here is the answer to your above question:
"Successful apps have the best app icons in common."
As it is said,
Books are judged by its cover. Similarly, apps are judged by its icons. Because icons are first noticed rather than its title.
Yes, app icons play a massively important part in terms of user's perception to an app and the number of downloads as well. Icons even responsible for CTR(Click Through Rate) in mobile application.
Apps get rejected from app Store just because of bad icon design. And if in case it is accepted, your app has to compete with 1.2 million other apps. You don't want your app icon to be drown in mundane. Designing the perfect app icon can make your app stand out of others.
How to make an app icon more magnificent with immediate recognizable appearance?
But Wait!
Prior designing an app icon, you must do a meticulous research on the market. Detailed study on your competitors will enable you to design such icon that withstands the competition.
Here are some tips for designing attractive and download-inducing app icons.