"Never judge a book by its cover."
We can throw that right out the window. We all do it, and no longer in books. In games, people often see a pretty icon and download it instantly. First impressions can be crucial, and you don't want your icon lacking quality, or your title unpronounceable.
What Makes a Good Icon?
Tell a story in 100x100 pixels. That can be hard, but it can also be a fun challenge. Let's talk through some popular games and their icons. Some of these are from FGL and their list of 100 best/worst icons.
Look at how bright and vibrant the colors are, as well as the contrast these icons make. You don't need to tell me anything about it, their looks alone would make me hit the download button. Might be the worst game ever, but overall, icons of this much quality usually end up being well made games.