Combine Concentration, Super Monkey Ball, and the long Internet tradition of infinitely extendable level-based puzzle games, and you might get something that approaches a shadow of the depth that Enigma (free). I've only begun to play and there's already more complexity than you find in many complete, but more casually oriented, games of this type.
What type, you ask? The type which I call "learning the world" games. You know. You start off with a simple goal and simple objects with simple rules. Then you add some more objects and behaviors. Then more. Then more and more and... well, Enigma has a lot of objects.
The goal is simple. (Hah!) You have a little black marble. You move your marble into a specially marked stone tile (except for when they're not specially marked) and it reveals a color. You then find another marked stone which has the same color. Click two 'red' or 'blue' in sequence, and they 'lock' open. Lock open all the colors and you win the level. Click a 'red', but then click a 'green', say, and the red 'closes'. You need to remember where the other green is, or find the other red, and so on.
Did I mention many of the maps extend well beyond the screen, requiring you to traverse vast mazes? Did I mention the one-way gates (which sometimes change direction based on rolling over other tiles somewhere else?) How about the tiles it's deadly to touch? The floors which slowly shrink your marble, so you can traverse them briefly but can't linger for long? The accelerator floors? The 'trampoline' tiles? The lasers? The dynamite??? A bouncy happy fun "give this to your grandma" puzzle game... this ain't.
Enigma works fine under Windows, but it's a multi-platform game designed by Linux programmers, and the interface is very non-Windows. There's no menu bar and once you're in the game window, your mouse cannot leave it until you hit "Esc" to get back to the game menu. You can set the window size (it cannot be resized in play) under Options, or play in full-screen mode, and adjust the sound and music volume as well.
There are over 1,000 levels included in the download, and more user created levels are being added all the time. It's all free--no unlock codes, no 'play 10 levels and then send us money' gimmicks. If you have any love of puzzle games and have good mix of a logical mind and some decent manual dexterity--this game requires a bit of mouse skill as well as thought--you will want to download Enigma.