Marble Arena 2 is a level-based 3D platformer game where the player controls a spinning marble. The mouse controls the view angle, and the keyboard controls the ball's acceleration in any direction. There is a built-in pack of official levels, which are unlockable one by one, as well as freely playable arcade and custom levels.
The goal on each level is to reach a minimum score, usually by collecting stars of various colors. Various obstacles, such as high walls, varied terrain, and gaps in the floor make this more difficult - and there are power-ups and special transportation devices to compensate.
Still, the official levels are much more challenging than they should be for a game that aims to be casual. The first level out of the tutorial, for instance, took me 15 minutes of frustration when it should have taken less than 5, and the second threw out everything the tutorial taught for a weird new scoring system that used soccer balls.
Also, I understand that a part of the challenge is that the ball's inertia makes it challenging to move with ease, but I found that it was as if the terrain was always covered with ice, even when it was supposed to have relatively high traction. Not a lot of fun.
Sam's Protip: Read the question mark tips closely, if they're present, because you will probably have no idea what you're supposed to be doing otherwise. And approach them slowly, because you keep your inertia after you finish reading.