Or as they put it on their official site:
In Symphony, you fight through levels uniquely generated by your own song collection, discover items and vanquish bosses to defeat the evil within! (…) In Symphony, each song in your collection not only becomes a unique level, but also provides you with an item you can equip and challenges you with score targets to reach. As you progress through the game, you unlock new difficulty levels, new items and abilities! This means you have many reasons to play your favorite song over and over.
Fortunately for the developers they actually manage to deliver on their promise.
Symphony gets the most important aspect of this genre of games right: the music scanning and level generation. Every song brings with it a unique experience full of enemies to vanquish and bullet-hell to avoid. Unlike Audiosurf, even slower songs provide very satisfying gameplay. What sets Symphony apart from other games in the genre, is the sense of progression. As you advance in the game, you can unlock difficulty levels, fight bosses and upgrade your ship. At the same time, the game is still highly accessible, allowing you to play in short bursts of time.
If the game has any issues they’re minor. Compared to other games in the genre, the actual scanning process of your music is lengthier. It’s recommended to allow the game to scan your entire music library before running it for the first time. Even then, it will still take a good couple of seconds to scan individual tracks before you play them. It’s only a matter of seconds but that’s noticeably longer than the near instantaneous gameplay of Audiosurf or Beat Hazard. The game as of now also doesn’t recognise Asian characters, which if you own a lot of J-Pop or K-pop can result in large parts of the game menu looking like the screenshot below.
Finally, Last.fm integration would be a great addition if only to satisfy the social data mining needs of todays hipster gaming youth. It’s not an absolutely crucial feature, but many other games in the genre have the feature built in, so it seems like a rather glaring omission not to include it.