I got this game as part of a Humble Bundle a couple of months ago and I regret not playing it until now.
The game struck me like Audiosurf before I played it (I didn't look at the store page)
I was horribly mistaken.
This game has one huge thing that Audiosurf did not. Purpose.
In audiosurf, you're just collectng blocks for the sake of it. There's no real rhyme or reason as to why you are, you just are.
In this game, you fight against monsters who use your music against you, taking it away, and making you weaker. The intro struck me because the game throws you straight in front of these two glowing eyes and a glitchy demon voice, explaining how, 'Music is the product of intelligent beings' and how it's his gateway.
You fight to free parts of "The Symphony of Souls" which was created by the demon, or whatever he is for that manner, and his subordinates, who, coincidentally, are abducted composers. Go figure.
The weapon system is very cool, the fact that you can choose four different weapons, each working a different way, to fight off the waves.
The leaderboard system is interesting as well, because, the weaker you are, the higher your base score multiplier.
You also unlock different difficulty levels as you free parts of the Symphony.
Now for the breakdown:
Built in song library
Fleshed out weapon system
Weapon Customization (Upgrades, Rotration, firing type, etc)
You Die, A Lot (Unlimited lives though)
Having your own music makes the geme more personal
Leaderboards don't always recognise songs
Mildly annoying firing effects
tl;dr Veterans and newbies alike will enjoy this game that fuses elements of classic vertical shooters, and rhythm games