Challenging and clever.

Circle Rider has the player in the role of an inventor who has just had his invention stolen, and must traverse 18 levels within a wormhole to obtain it. The game has a very unique gameplay mechanic in the form of an adjustable circle which the ball-like player character can travel around the circumference of. This gimmick is used to great effect, especially in the harder levels. Nice quirky gameplay variations are thrown in for good measure, such as flipping from one side of the circle to the other, and a moving line on which the circle travels.

The controls work well--you'll use the left and right arrow keys to travel around the circle, and can adjust the size of it with the up and down keys. Though your circle will remain stationary for the early levels, leaving you time to think things through, later you'll be required to time your size-changes and circumference movement when it becomes attached to a moving line, with spiked walls lying in wait to trap you.

The background music is a quite nice, soft-rock-style track with a solid melody and some great compositional work. Graphic-wise, the game is simple, but has its own charming style. It's short enough to be beaten in just a few sittings or less, depending on how good you are. I'd actually rather have it short instead of getting bored by fifty long levels, so the playing time ends up working out fine.

The challenge ramps up towards the end, and you'll end up dying multiple times in frustration, but overall, Circle Rider a unique, charming arcade game that's definitely worth a playthrough.