There was a time when it was simply taken for granted that mobile games were simple, casual distractions.
But with the changes in both the capabilities of mobile devices and the culture of mobile gaming, it's now often the titles with the depth to engage players over longer periods that bring in greater profits.
Is there always a need to complicate things, though? One company that's kept faith in simple, single-mechanic games is Ketchapp, whose business was deemed healthy enough to be acquired by Ubisoft in 2016.
Another publisher of casual games competing in the same space is Voodoo. In early January, games from Ketchapp and Voodoo made up eight of the 10 most downloaded iPhone games in the UK that week.
And while its business model is slightly different, with games developed in-house and an increasing move towards IAP over ad-based monetisation, Gram Games is another company that's become known for its sharp, casual games based around one strong idea.
Volume is key
First, it's important to understand the model. Take 2048, one of Ketchapp's biggest and most recognisable titles. This will never be a game that rivals Clash of Clans or Star Wars: Galaxy of Heroes in the grossing charts, but nor does it need to.
If you're getting this many eyes on in-game ads, you don't need thousands in IAP revenue.
The time and resources expended on its initial development were only a fraction of what went into the above games (especially since 2048 is a fairly transparent clone of the earlier Threes), and the need for post-release support is minimal.
But it's a game that's been downloaded millions of times and, as App Annie data shows, appeared at 534th in the US iPhone downloads chart on January 11th 2018 - nearly four years after its original launch.
If you're getting this many eyes on in-game advertisements, and doing it at scale with a number of other games at the same time, then you don't necessarily require thousands of dollars in IAP revenue to create a sustainable business.
Because of this, and the fact that many of the featured games don't even include IAPs, here we will focus on the download charts rather than grossing ranks. The latter is also insufficient for ranking these kinds of games as it cannot account for advertising revenue.
This is part of an issue raised by user acquisition expert Eric Seufert on whether app intelligence firms are offering relevant enough data as ad-monetisation becomes more popular.
Keeping it fresh
While legacy games like 2048 may still be picking up some downloads for Ketchapp, its business really relies on new releases.
One of the firm's latest is Balls Race, launched on January 3rd, which has been among the top 10 most downloaded iPhone apps in the US since the day after its release. On January 8th and 9th the game topped the charts.
Its games may look increasingly rudimentary in the modern mobile market, but Ketchapp's first release of 2018 is already proving that the company still knows how to generate downloads.
The downside, however, is shown by another recent Ketchapp launch. Fit launched at 20th in the US iPhone download charts on December 20th 2017, ranking at 14th and 15th in the following two days.
But then - possibly influenced by the Christmas period - the game began a consistent descent. By December 30th the game was at 281st, and by January 6th - the last day it registered a chart position - it had sunk to 1,402nd.
That's the danger of an overnight success: it can go as quickly as it came. For Ketchapp, at least, there's always another game just around the corner. Though it could be argued that the plethora of short-term downloads is worth the effort in the hyper-casual market.
No doubt learning from Ketchapp is Voodoo, a company which announced itself in late 2016 with Paper.io.
That game was a slow burn compared to others in this article, only really rising through the ranks in late December and early January.
On January 22nd 2017 the game notched what is to date its highest position in the iPhone downloads chart, hitting second.
Nearly one year on, January 10th 2018, the game is still seeing a significant number of downloads with a rank of 153rd.
Paper.io also features in-app purchases, and though it's hardly dominated the grossing charts, a pretty consistent presence suggests their inclusion has been worthwhile.
The game peaked at 321st in the US iPhone grossing charts in February 2017, and as of January 8th 2018 it sat at 1,310th.
Another Voodoo title that's stuck around - though not so much in terms of grossing - is Flappy Dunk.
Still at 157th in the US iPhone downloads charts on January 10th 2018, several months on from its May 2017 launch, there's a suggestion here that perhaps the shelf life for hyper-casual mobile games is longer than often imagined.
Risk versus reward
As mentioned before, Gram Games does not fit quite so neatly in this category. For one, its games are rather more complex than those of Ketchapp and Voodoo. It also releases significantly fewer of them.
But games like 1010! and Merged! fit the mould of being simple, casual games that monetise primarily through advertising.
Just as Voodoo's breakthrough hit was Paper.io, Gram Games' was 1010!. Launched in 2014, the game began to rise up the US iPhone download charts in 2015 and still has a presence today. As of January 10th 2018, it was ranked 852nd.
But the firm's more recent titles, Bounzy! and the relaunched Merged Dragons!, have failed to hit the same heights and dropped off quickly, with respective ranks of 1,404th and 1,006th on the US iPhone downloads charts on January 10th 2018.
But Merge Dragons!, at least, has been a good introduction to IAP monetisation for the company. It's peaked inside the top 200 on the US iPhone grossing charts, ranking at 232nd as of January 10th 2018.
The question, then, is which direction does Gram Games wish to go? The rewards may be greater with IAP-funded games, but so too are the risks.
The approaches of Ketchapp and Voodoo may not yield top grossing hits - at least by the IAP-focused data that's available - but they are also resilient to individual failures in a way that few other mobile games companies are capable of being.
For more on hyper-casual games, check out our three-part series on the ascendance of hyper-casual by AppLovin's Johannes Heinze.