This game is freakin' addictive. When you combine twin-stick shooter mechanics with intense music-driven gameplay, you get Beat Hazard. Everything from the explosions to the type of enemies you encounter are all affected by the beat of the music. There's more to it as well. You can collect power-ups, get multipliers to increase your score and, of course, you can use your own music (You have to buy iTunes support, but it's only a dollar, so literally a small price to pay). You can also rank up and get perks that can give you a leg-up to shooting up the leaderboards. And then there's the DLC (Ultra and Shadow Operations) which add new ships, enemies, missions (getting [x] amount of points or completing [x] amount of songs on a certain difficulty) and even Steam Workshop support, letting you download even more ships and missions. Pausing's a little weird, however; with an Xbox 360 controller you have to press both Start and Back to pause. Other than that, this is easily one of the best music-driven games I've played. If you're tired of Audiosurf and want something different, this is for you.
A word of warning, however: There are LOTS of flashing lights and visuals in this game (it even warns you when you start the game). So if you suffer for photosensitive seizures or the like, then you should avoid this game (Then again, if you suffer from such a condition, you shouldn't be playing games in the first place).