You don't have a sales or signup funnel of any kind. Don't just drop users into the heart of your app. What if they don't know what Sudoku is or how to play it?

You don't have a sales or signup funnel of any kind. Don't just drop users into the heart of your app. What if they don't know what Sudoku is or how to play it? They will just leave. When you signup for World of Warcraft or League of Legends, two of the most popular games in the world, do they just dump you into a game? Nope. They gradually help you engage with the game while simultaneously teaching you what you need to know along the way. By the time a user reaches the end of their funnel and gains a few levels or achievements, they are addicted and will come back on their own. Getting a funnel right is extremely difficult, but worth the effort.