This is a Sonic the Hedgehog version of the classic "match the pairs of hidden pictures" memory game.
There are 80 Sonic picture cards (so that's 40 pairs of pictures to match) comprising 10 different Sonic characters, each appearing 8 times in the 10 x 8 game grid. Successfully matching pairs of the picture cards will slowly reveal a much larger random bonus Sonic picture in the game grid. There are 3 different "level" themes to choose from, each one featuring a different piece of background music from 3 classic levels of the first ever Sonic game that appeared on the Sega Mega Drive/Genesis in 1991.
The object of the game is simple but challenging: clear the game grid by matching all the hidden picture pairs in the fastest time, and in the least number of moves, as you possibly can. Your best score will be stored locally on your computer for future reference (and there is a reset option to clear that later if you ever want to). Also, just in case you want it, a "World Top 10" high-scores table version of the game is available at MarioSonicGames dot com - click on the link in the game to get to the site.