When your replay is limited by the amount of music you own, and you own a whole lot of music, then you're all set.
Audiosurf is the perfect game for when you find yourself unable to decide what to play. You may just want to relax and listen to some chill music, or you may find yourself wanting to rave with nobody around. Either way, Audiosurf will take your music tracks and your choice of difficulty, and put them together to create a spectacular showcase.
There are even multiple modes to play. My choice is always the Eraser on the hardest difficulty, with ironmode on just to feel a bit more awesome about myself. The Eraser has the ability to erase all of one colored block from your entire queue.
The leaderboards make the game even more addicting. When you get an email telling you that someone is better at Stay Don't Go by Spoon than you are, you find yourself instantly back on Audiosurf trying to collect every last yellow and red block to shoot your score back on top.
The innovation of this game is definitely underappreciated. Rockband and Guitar Hero bring you a set list of songs that have tracks with them. Audiosurf on the other hand, can be any track you want. It doesn't even have to be music if you don't want. Audiosurf can take that recorded Obama speech and create a track highlighting all his speech highs and lows. The next step would be to meld the two games together, and create on the fly instrument tracks for any song.
Overall, Audiosurf has been one of the longest lasting PC games that I've ever played, and I'm sure it will continue to be until the next one is created.