How it came into my hands: I went to download the demo, and discovered that it is only available through this weird framework called Steam. I'd heard mixed things about Steam, but I went and read all the small print carefully and decided it was a minor degree of evil that I could live with. I don't like DRM, but DRM for games makes some amount of sense, much more so than for music or texts.
The demo is extremely limited, letting you play only four games. I think an hour's play is reasonable, or a month with limitations on which game features you can access. Having an excessively restricted demo like that makes me reluctant to buy the full version; I was still getting the hang of the controls after four plays and couldn't tell if I was going to like the game or not. But it was on special offer of $5, (normal price $10), and that's impulse purchase money for me, so I just went ahead and bought it.
Verdict: Audiosurf is just the kind of addictive casual game I like.
Audiosurf is essentially a cross between Guitar Hero and Klax. Seriously. As such, it's going to appeal to people who like casual, Tetris-ish games, which I very much do, but like the original Klax it's a lot more based on reflexes than strategy. The music analysis element gives it an original and highly playable twist, and I would judge that it has a much higher replay potential than a typical casual game. Since it autogenerates tracks based on various features of the music, the variety of levels is almost unlimited.
The music analysis is pretty good, but perhaps could be better. For example, the normalization works really well, so that relatively fast sections of slow songs make downhill sections and vice versa, and it can pick out the major beat from a background of a lot of unmanageably rapid noise. The way that beats and melody are translated into features of the track or the traffic works really well to make a playable and varied game. It's a bit hit-and-miss about picking up beats that aren't marked by drums, but syncopated music makes for a really interesting game when the system manages to read it correctly. The instructions suggest using a song with a prominent beat; I found that some where the beat really dominates (eg Joy Division) just make me Doom-sick, but that probably varies a lot between individuals. It seems like romantic goth stuff (All About Eve, for example) works best; there is a strong beat but the variation in tempo of the melody makes for lots of interesting track features. The powerups and medals and so on generally enhance the game, but they're minor frills.
I think I would like this game a lot better if it were stand-alone rather than being tied to Steam. It's kind of cute to be able to compare your scores with other players using the system, but there is no multiplayer functionality (and given the nature of the game it would be rather difficult to arrange one). I would much prefer being able to see detailed stats about my own performance, which the game doesn't provide at all; if you play a song you've already tried, it will tell you your personal best, but there's no way to get a table of all the scores you've achieved recently, let alone fun things like averages or records. Also, the whole thing is fantastically slow to load; I may be nostalgic for my 80s childhood, but not for the part where you had to wait 5 minutes while the computer read data from a tape! In this case it's waiting for Steam to contact the internet, make sure you have a valid subscription and the latest updates and do whatever not exactly spyware reporting tasks it needs to do. That would be worth it if it were properly multiplayer, but as it is it's just annoying.
The thing is very memory hungry; on my two year old laptop I have to close everything else for it to play smoothly. I don't think that's due to the maths; I'm content to wait a few tens of seconds while it converts a song into a track, so it's not doing Fourier Transforms on the fly or anything, though I suppose it is doing graphics at the same time as acting as a music player. I suspect that running Steam in the background is eating a lot of processing power, though.
Anyway, yes, I confess myself thoroughly addicted! Between this and accidentally rediscovering the Distributed Proofreaders adjunct to Project Gutenberg, I'm having a hard time making progress on my grant application...