You awake in an ocean. In front of you is an island painted in vibrant colours, speckled with woods and ruins, meadows and mountains. You swim towards it. Wading onto the shore causes music to play. This music comprises how you interact with the world, altering depending on where you're stood, the time of day, the weather, the animals you chase, and the season.

Functionally, that's more or less it. How Proteus works can be summarised in a single, brief paragraph. Explaining why it works, however, would probably require some kind of psychological study, because all my prior experience as a gamer tells me it shouldn't.The developer, Ed Key, explains that this initial response is fairly common: "There's a general thing where someone says 'I played it for 5 minutes and I was about to turn it off. I thought it was pointless. But then something sucked me in and forty minutes later I was still exploring it.' Those times when someone doesn't think they'll like it but they find themselves engaged, those are the most rewarding." Proteus began life as a more straightforward RPG, but took a dramatic shift in development with the arrival of musician David Kanaga a year into the project. "The music thing came about really quickly." Ed says. "Looking at the exchange of emails between me and David, it was like three or four emails. It was mostly David's idea, that 'Let's try this and see if it will work.' But it very quickly solidified."This reactive, layered musical score is designed to motivate the player's exploration of the island. Different landscapes and objects emit ambient sounds that gradually shift and build upon each other. Traversing a thicket of trees in summertime generates a score bursting with beats and rhythms and jaunty harmonies. Conversely, stand atop a hill at midnight and the world is eerily silent, with only the rushing wind carrying the odd mournful note across the barren summit.More direct melodic interaction can be made through the curious wildlife. Frogs hop along an invisible keyboard if you chase them, and bizarre mushroom-like creatures leap into the sky with a glittering trill as you approach. Ed and David are spending a few more months filling it with as much life as possible."There's one I'm working on at the moment which has – I totally reserve the right to change this – its own musical system that's inspired by Skylarks, which have a very complex melodic pattern. It's a cross between that and an excitable dog, which runs off into the distance and then runs back to see where you are. So it's a slightly more complex and more sociable AI than most creatures have at the moment."While there is a form of progression that I'll avoid discussing directly, there's no determinate objective. It's about exploring at your own pace, finding your own rhythm to the game's beat. "I almost hope that I can infect their mind with lazy wandering virus and they'll just go out and wander about," Ed jokes.There are also plans to make this exploration more sociable by coding screenshots into what are essentially save-games players can share. "There's a little elaboration on that, where there'll be some kind of traces and trails of the person who took the screenshot. So it's like a little bit of memory. The idea is if you then take a screenshot from a world that came from a screenshot and pass that on, then it will have your traces and the other person's traces."What surprised me most about Proteus was I found myself going back to it over and over. There's something delightfully intoxicating about it, something unique and intriguing about its design and ideas. Most of all, though, it's just genuinely pleasant. That's an adjective that doesn't get used enough when talking about games.

Rick Lane is a freelance contributor and musical frog chaser for various websites and magazines. Hisfeed does not have an ambient soundtrack, but you might want to follow it anyway.