Sometimes there's no telling what will become popular in the world of app gaming. Angry Birds, probably the most popular app game of all time—so popular in fact that it's getting its own film adaptation—took a repetitive, familiar format that had long existed at online arcades and turned it into a mobile sensation. Crossy Road, one of the most downloaded gaming apps of late, is little more than a creative adaptation of Frogger, one of the oldest arcade games in existence! Basically, it can be unpredictable what sparks a hit, or in the case of those two examples, an international sensation.

Casting aside predictions about which individual games might top the charts at a given time and looking instead at broader trends in app stores, we can begin to get an idea of what the next wave of trends in this industry will look like. These are some that come to mind.

Open World Apps

If the concept of an open world video game on a mobile app sounds a little out there, you may want to think twice, because plenty of these games actually already exist. This YouTube list of the best open world app games was compiled over a year ago, and it makes it surprisingly clear just how many of these games are available. But there's also a chance they're just getting started. Just think of the progress that's been made in between Grand Theft Auto III and the likes of Skyrim or some of the games announced at E3. This progress is admittedly due in large part to the transition to current generation gaming consoles, but it's also a model for a budding genre in apps. As developers grow bolder and phones and tablets more capable, don't be surprised if this becomes a very expansive genre.

Real Casino Apps

Casino apps already comprise a pretty significant corner of the app gaming market, but for the most part they're gimmicks and imitations. What you may not realise is that more legitimate options associated with established online casinos already exist, and they're growing more prevalent. The mobile platform for Gala Bingo offers a wide range of bingo, slot machine, and other casino games to users, and as the online casino industry continues to grow, apps like these are only going to become more common. In particular, expansion into the United States market—conceivable in the next few years—could lead to a boom in these apps all around the world.

Atmospheric Apps

That's a very broad description, and yet it speaks to a lot of the elements that are at the foundation of some of the most popular and successful apps. As our mobile devices have grown more capable, users have begun to look more for sharp visuals, quality sound, and receptive touch. The games that exemplify these traits consistently stand out. Look through Stuff's list of the best iOS games and you'll find a number that are notable specifically due to atmosphere: Year Walk, The Room, Device 6, and several others. Recently we've even seen the successful release of an app game (A Blind Legend) that operates entirely by sound, creating an atmosphere around you without any visuals. As it becomes clearer and clearer that games like these are well received by players, there will only be more of them in stores.

Again, there's no telling exactly which games will become popular and when. However, these categories are almost certain to grow even more popular than they already are in the coming years.