Attached to a wall at Ustwo Games' London studio is one of the team's favourite user reviews for Monument Valley.
It says: "Thank you for making this game, I thought it was really beautiful, one of the best things I've played on mobile, and it really impacted me. I just thought £3.99 was too much."
"That's always been super funny to us," chief creative officer Dan Gray tells GamesIndustry.biz.
Amusing as it is, it illustrates the biggest challenge of the mobile space: the value players place on games. Following the launch of the App Store, a race to the bottom means that the vast majority of mobile titles are now free-to-play..
Premium is still an option, of course, as Ustwo has demonstrated with Monument Valley -- the sequel to which made $10 million in its first year. But Gray acknowledges this is not the norm.
"Making premium games has been a dangerous proposition for a number of years," he says. "Even we know we were very lucky with Monument Valley. We were lucky to get a unicorn, but the exception doesn't prove the rule. It would still be dangerous for us now to throw a game out there and charge £5."