A short time ago I discovered a game called "Audio-surf" which can be bought for 10$ via Steam by Valve. At the moment this are not more than 5€ which are well spend in my opinion. But what's this game about?
Before it start you have to chose a mp3 file (or another file in one of the supported formats). This will be analyzed with some weird algorithms and it will be build a kind of race course out of it. Now you have to collect colored blocks on this course which are arranged according to the beat and signifcant notes. To put it simple: The more blocks you collect the more points you get. After you completed the song you can compare to the world best in a high score list, which is created for every song.
Most fascinating is how perfect the analysis of the songs is. No matter which music genre you chose, the intense moments and calm phases will be identified accuratly, the game speed will be adjusted to the music speed and arrangement of the blocks matches every significant note.
Moreover you can chose roundabout a dozen different character. These are mainly different difficulties and game modes. Among other things there is on mode for two player at one PC.
I think everyone could by this game, because 10$ are not that much and you get a great reward – whether you like it more to get the highest score or more to relax. By the way: You will also get the whole Half-Life and Portal sound track with this game for free!
PS: Just take a look at Youtube and search for Audio-surf. You will find a bunch of movies from this game!