Side-scrolling auto-running platformers are certainly not a rare game type on mobile. Between Jetpack Joyride, the Rayman series, the original Alto's Adventure, and countless others, most of us probably own a few games like this already.
The biggest way Alto's Odyssey differentiates itself from the rest of the field is through its beautiful, relaxing, peaceful atmosphere. Everything about the presentation - the gentle sunrise, the use of simple silhouettes against smooth background colors, the perfectly-matched sound effects - the whole thing creates an almost zen-like feeling.
The other big way Alto's Odyssey differentiates from the rest of the games out there: quality. Everything about this game feels like its been tested, polished, and retested hundreds of times, until it couldn't possibly be improved any further. It is a rare feeling these days, where the trend is to launch games in an incomplete and buggy state, then push a bunch of updates to bring things up to par. Alto's Odyssey feels like a game that is perfect exactly as it is, and although I'm sure it'll receive the occasional update, absolutely nothing about it needs an update.
Honestly, I could go on and on about why this is such an amazing game, but there are enough stories like that already. Federico Viticci at MacStories wrote a wonderful article describing the feelings and emotions this game can engender. TouchArcade gave Alto's Odyssey their game of the week, and a glowing review. Review aggregator Metacritic currently lists Alto's Odyssey at a score of 91 out of 100. Our Twitter timelines are full of people posting their high scores and commiserating over bad-beat stories.
Everyone is playing and loving Alto's Odyssey, and that fills me with enthusiasm about the state of mobile gaming. Premium games - games where you pay an upfront fee to get a great experience - have always been what I gravitate towards, as a player. When one this good comes out, and does this well, it lends creedence to the model of selling great games. ArsTechnica has a great interview with Alto's creators about just how much went into making such a great mobile game, which is definitely worth reading for anyone interested in premium mobile gaming, and some of the ways in which Alto's creators approached iOS.
Games this good don't show up often. An extremely polished, pay-once, premium game like this is a bit of an anachronism in 2018. If more games take a page from Alto's Odyssey, I think the App Store would be a much better place.