iO is a 2D physics puzzle game where you are tasked with rolling a ball from A-to-B. The key to getting to the objective is keeping your momentum going by growing and shrinking in size, which directly affects your movement speed. Sounds simple enough, however there are multiple obstacles along the way that are designed to slow or even stop you in your tracks.

The controls are as simplistic as it gets: you use the left analogue stick to roll left and right and you use the right analogue stick to grow or shrink the size of the ball. The main mechanic used to solve puzzles or get over obstacles is changing your size; this can affect your speed, weight, and view of the level. Your timing is the key to keeping your momentum: growing when falling and shrinking when being launched upward is the simplest of rules to get to grips with. Every time you shrink in size the camera will zoom in really far, restricting your view of the level; this gives you less time to react to obstacles and also makes it difficult to get your timing spot on.

The entire game is level-based with 225 levels altogether, each usually lasting only a couple of minutes to complete. The levels begin simple enough, teaching you the basic physics to growing and shrinking by having you cross larger and larger gaps. Then it'll send you round loops and up walls, progressively getting harder as you progress. Towards the later levels in the game the difficulty is really ramped up with the addition of red areas that reset you to the start when touched, moving platforms and also portals that teleport you across the level. This high difficulty spike certainly catches you off guard and the lack of help from the game means that we found a large number of the levels unpassable. Thankfully you are able to pick and choose to play the levels in whatever order you like.

Visually the game is very minimalistic taking a similar style to that of Line Rider, with simple coloured lines drawn onto a black background for you to traverse. Although there isn't much to look at, the cleanliness and clarity in marking out where you are and where you need to get to is rather pleasant.

Although the physics of the game feel solid, the majority of the level designs feel like they rely too heavily on trial and error and good fortune rather than skill. For instance one level requires you to juggle a cube on top of your ball and move it from one platform to another without allowing it to lose height. This level took us many attempts until we just got it purely by luck.

Conclusion

iO is a solid physics puzzler with simple controls, minimalistic visuals, and challenging gameplay that comes together as an overall decent experience. The tough difficulty spike and puzzles reliant on trial and error and good luck prevent this from being an excellent title, but if you are looking for a game to roll you over to the next big release then this is certainly worth a punt.